.. Automatically generated by example2rst.py.  Do not edit this file

.. currentmodule:: apsw

Example/Tour
============

This code demonstrates usage of APSW.  It gives you a good overview of
all the things that can be done.  Also included is output so you can
see what gets printed when you run the code.

There are also specific examples in the classes, functions,
and attribute documentation.

.. code-block:: python

   #!/usr/bin/env python3
   
   # This code uses Python's optional typing annotations.  You can
   # ignore them and do not need to use them.  If you do use them
   # then you must include this future annotations line first.
   from __future__ import annotations
   
   from typing import Optional, Iterator, Any
   
   import os
   import sys
   import time
   import datetime
   import apsw
   import apsw.ext
   import random
   import re
   from pathlib import Path
   
   # pretty formatting
   from pprint import pprint
   

.. index:: Checking APSW and SQLite versions (example code)

.. _example_version_check:

Checking APSW and SQLite versions
---------------------------------


.. code-block:: python

   # Where the extension module is on the filesystem
   print("      Using APSW file", apsw.__file__)
   
   # From the extension
   print("         APSW version", apsw.apsw_version())
   
   # From the sqlite header file at APSW compile time
   print("SQLite header version", apsw.SQLITE_VERSION_NUMBER)
   
   # The SQLite code running
   print("   SQLite lib version", apsw.sqlite_lib_version())
   
   # If True then SQLite is incorporated into the extension.
   # If False then a shared library is being used, or static linking
   print("   Using amalgamation", apsw.using_amalgamation)
   


.. code-block:: output

          Using APSW file /space/apsw/apsw/__init__.cpython-312-x86_64-linux-gnu.so
             APSW version 3.47.2.0
    SQLite header version 3047002
       SQLite lib version 3.47.2
       Using amalgamation True


.. index:: Best Practice (example code)

.. _example_bestpractice:

Best Practice
-------------

Ensure SQLite usage prevents common mistakes, and gets best
performance via :doc:`apsw.bestpractice <bestpractice>`

.. code-block:: python

   import apsw.bestpractice
   
   apsw.bestpractice.apply(apsw.bestpractice.recommended)
   

.. index:: Logging (example code)

.. _example_logging:

Logging
-------

It is a good idea to get SQLite's logs as you will get more
information about errors. Best practice also includes this.
:meth:`apsw.ext.log_sqlite` forwards SQLite's log messages to the
:mod:`logging` module.

.. code-block:: python

   apsw.ext.log_sqlite()
   
   # You can also write to SQLite's log
   apsw.log(apsw.SQLITE_ERROR, "A message from Python")
   

.. index:: Opening the database (example code)

.. _example_open_db:

Opening the database
--------------------

You open the database by using :class:`Connection`

.. code-block:: python

   # Default will create the database if it doesn't exist
   connection = apsw.Connection("dbfile")
   
   # Open existing read-only
   connection = apsw.Connection(
       "dbfile", flags=apsw.SQLITE_OPEN_READONLY
   )
   
   # Open existing read-write (exception if it doesn't exist)
   connection = apsw.Connection(
       "dbfile", flags=apsw.SQLITE_OPEN_READWRITE
   )
   

.. index:: Executing SQL (example code)

.. _example_executing_sql:

Executing SQL
-------------

Use :meth:`Connection.execute` to execute SQL

.. code-block:: python

   connection.execute("create table point(x,y,z)")
   connection.execute("insert into point values(1, 2, 3)")
   # You can use multiple ; separated statements
   connection.execute(
       """
       insert into point values(4, 5, 6);
       create table log(timestamp, event);
       create table foo(a, b, c);
       create table important(secret, data);
   """
   )
   
   # read rows
   for row in connection.execute("select * from point"):
       print(row)
   


.. code-block:: output

    (1, 2, 3)
    (4, 5, 6)


.. index:: Why you use bindings to provide values (example code)

.. _example_why_bindings:

Why you use bindings to provide values
--------------------------------------

It is tempting to compose strings with the values in them, but it is
easy to mangle the query especially if values contain punctuation
and unicode.  It is known as `SQL injection
<https://en.wikipedia.org/wiki/SQL_injection>`__. Bindings are the
correct way to supply values to queries.

.. code-block:: python

   # a simple value
   event = "system started"
   # DO NOT DO THIS
   query = f"insert into log values(0, '{ event }')"
   print("query:", query)
   
   # BECAUSE ... a bad guy could provide a value like this
   event = "bad guy here') ; drop table important; -- comment"
   # which has effects like this
   query = f"insert into log values(0, '{ event }')"
   print("bad guy:", query)
   


.. code-block:: output

    query: insert into log values(0, 'system started')
    bad guy: insert into log values(0, 'bad guy here') ; drop table important; -- comment')


.. index:: Bindings (sequence) (example code)

.. _example_bindings_sequence:

Bindings (sequence)
-------------------

Bindings can be provided as a sequence such as with
a tuple or list.  Use **?** to show where the values go.

.. code-block:: python

   query = "insert into log values(?, ?)"
   data = (7, "transmission started")
   connection.execute(query, data)
   
   # You can also use numbers after the ? to select
   # values from the sequence.  Note that numbering
   # starts at 1
   query = "select ?1, ?3, ?2"
   data = ("alpha", "beta", "gamma")
   for row in connection.execute(query, data):
       print(row)
   


.. code-block:: output

    ('alpha', 'gamma', 'beta')


.. index:: Bindings (dict) (example code)

.. _example_bindings_dict:

Bindings (dict)
---------------

You can also supply bindings with a dictionary.  Use **:NAME**,
**@NAME**, or **$NAME**, to provide the key name in the query.
Names are case sensitive.

.. code-block:: python

   query = "insert into point values(:x, @Y, $z)"
   data = {"x": 7, "Y": 8, "z": 9}
   connection.execute(query, data)
   

.. index:: Transactions (example code)

.. _example_transaction:

Transactions
------------

By default each statement is its own transaction.  A transaction
finishes by flushing data to storage and waiting for the operating
system to confirm it is permanently there (ie will survive a power
failure) which takes a while.

.. code-block:: python

   # 3 separate transactions
   connection.execute("insert into point values(2, 2, 2)")
   connection.execute("insert into point values(3, 3, 3)")
   connection.execute("insert into point values(4, 4, 4)")
   
   # You can use BEGIN / COMMIT to manually make a transaction
   connection.execute("BEGIN")
   connection.execute("insert into point values(2, 2, 2)")
   connection.execute("insert into point values(3, 3, 3)")
   connection.execute("insert into point values(4, 4, 4)")
   connection.execute("COMMIT")
   
   # Or use `with` that does it automatically
   with connection:
       connection.execute("insert into point values(2, 2, 2)")
       connection.execute("insert into point values(3, 3, 3)")
       connection.execute("insert into point values(4, 4, 4)")
   
   # Nested transactions are supported
   with connection:
       connection.execute("insert into point values(2, 2, 2)")
       with connection:
           connection.execute("insert into point values(3, 3, 3)")
           connection.execute("insert into point values(4, 4, 4)")
   

.. index:: executemany (example code)

.. _example_executemany:

executemany
-----------

You can execute the same SQL against a sequence using
:meth:`Connection.executemany`

.. code-block:: python

   data = (
       (1, 1, 1),
       (2, 2, 2),
       (3, 3, 3),
       (4, 4, 4),
       (5, 5, 5),
   )
   query = "insert into point values(?,?,?)"
   
   # we do it in a transaction
   with connection:
       # the query is run for each item in data
       connection.executemany(query, data)
   

.. index:: Pragmas (example code)

.. _example_pragma:

Pragmas
-------

SQLite has a `wide variety of pragmas <https://www.sqlite.org/pragma.html>`__ to control
the database configuration and library behaviour.  See the :doc:`tips` for maintaining
your schema.

.. code-block:: python

   # WAL mode is good for write performance
   connection.pragma("journal_mode", "wal")
   
   # Foreign keys are off by default, so turn them on
   connection.pragma("foreign_keys", True)
   
   # You can use this to see if any other connection (including other processes) has
   # changed the database
   connection.pragma("data_version")
   
   # Useful at startup to detect some database corruption
   check = connection.pragma("integrity_check")
   if check != "ok":
       print("Integrity check errors", check)
   

.. index:: Tracing execution (example code)

.. _example_exectrace:

Tracing execution
-----------------

You can trace execution of SQL statements and their bindings.  This
involves code changes and is :ref:`described in more detail here
<tracing>`.

There are simpler convenient mechanisms for :ref:`individual
statement tracing <example_Trace>`, :Ref:`summarising a block of
code <example_ShowResourceUsage>`, and :ref:`SQLite's interface
<example_trace_v2>` which is used by them.

.. code-block:: python

   
   def my_tracer(
       cursor: apsw.Cursor,
       statement: str,
       bindings: Optional[apsw.Bindings],
   ) -> bool:
       "Called just before executing each statement"
       print("SQL:", statement.strip())
       print("Bindings:", bindings)
       return True  # if you return False then execution is aborted
   
   
   # you can trace a single cursor
   cursor = connection.cursor()
   cursor.exec_trace = my_tracer
   cursor.execute(
       """
           drop table if exists bar;
           create table bar(x,y,z);
           select * from point where x=?;
           """,
       (3,),
   )
   
   # if set on a connection then all cursors are traced
   connection.exec_trace = my_tracer
   # and clearing it
   connection.exec_trace = None
   


.. code-block:: output

    SQL: drop table if exists bar;
    Bindings: ()
    SQL: create table bar(x,y,z);
    Bindings: ()
    SQL: select * from point where x=?;
    Bindings: (3,)


.. index:: Tracing returned rows (example code)

.. _example_rowtrace:

Tracing returned rows
---------------------

You can trace returned rows, including modifying what is returned or
skipping it completely.  See :ref:`more about tracing <tracing>`.

.. code-block:: python

   
   def row_tracer(
       cursor: apsw.Cursor, row: apsw.SQLiteValues
   ) -> apsw.SQLiteValues:
       """Called with each row of results before they are handed off.  You can return None to
       cause the row to be skipped or a different set of values to return"""
       print("Row:", row)
       return row
   
   
   # you can trace a single cursor
   cursor = connection.cursor()
   cursor.row_trace = row_tracer
   for row in cursor.execute("select x,y from point where x>4"):
       pass
   
   # if set on a connection then all cursors are traced
   connection.row_trace = row_tracer
   # and clearing it
   connection.row_trace = None
   


.. code-block:: output

    Row: (7, 8)
    Row: (5, 5)


.. index:: Defining scalar functions (example code)

.. _example_scalar:

Defining scalar functions
-------------------------

Scalar functions take one or more values and return one value.  They
are registered by calling :meth:`Connection.create_scalar_function`.

.. code-block:: python

   
   def ilove7(*args: apsw.SQLiteValue) -> int:
       "A scalar function"
       print(f"ilove7 got { args } but I love 7")
       return 7
   
   
   connection.create_scalar_function("seven", ilove7)
   
   for row in connection.execute(
       "select seven(x,y) from point where x>4"
   ):
       print("row", row)
   


.. code-block:: output

    ilove7 got (7, 8) but I love 7
    row (7,)
    ilove7 got (5, 5) but I love 7
    row (7,)


.. index:: Defining aggregate functions (example code)

.. _example_aggregate:

Defining aggregate functions
----------------------------

Aggregate functions are called multiple times with matching rows,
and then provide a final value.  An example is calculating an
average.  They are registered by calling
:meth:`Connection.create_aggregate_function`.

.. code-block:: python

   
   class longest:
       # Find which value when represented as a string is
       # the longest
   
       def __init__(self) -> None:
           self.longest = ""
   
       def step(self, *args: apsw.SQLiteValue) -> None:
           # Called with each matching row
           for arg in args:
               if len(str(arg)) > len(self.longest):
                   self.longest = str(arg)
   
       def final(self) -> str:
           # Called at the very end
           return self.longest
   
   
   connection.create_aggregate_function("longest", longest)
   print(connection.execute("select longest(event) from log").get)
   


.. code-block:: output

    transmission started


.. index:: Defining window functions (example code)

.. _example_window:

Defining window functions
-------------------------

Window functions input values come from a "window" around a row of
interest.  Four methods are called as the window moves to add,
remove, get the current value, and finalize.

An example is calculating an average of values in the window to
compare to the row.  They are registered by calling
:meth:`Connection.create_window_function`.

This is the Python equivalent to the C based example in the `SQLite
documentation
<https://www.sqlite.org/windowfunctions.html#user_defined_aggregate_window_functions>`__

.. code-block:: python

   
   class SumInt:
       def __init__(self):
           self.v = 0
   
       def step(self, arg):
           print("step", arg)
           self.v += arg
   
       def inverse(self, arg):
           print("inverse", arg)
           self.v -= arg
   
       def final(self):
           print("final", self.v)
           return self.v
   
       def value(self):
           print("value", self.v)
           return self.v
   
   
   connection.create_window_function("sumint", SumInt)
   
   for row in connection.execute(
       """
           CREATE TABLE t3(x, y);
           INSERT INTO t3 VALUES('a', 4),
                                ('b', 5),
                                ('c', 3),
                                ('d', 8),
                                ('e', 1);
           -- Use the window function
           SELECT x, sumint(y) OVER (
           ORDER BY x ROWS BETWEEN 1 PRECEDING AND 1 FOLLOWING
           ) AS sum_y
           FROM t3 ORDER BY x;
       """
   ):
       print("ROW", row)
   


.. code-block:: output

    step 4
    step 5
    value 9
    ROW ('a', 9)
    step 3
    value 12
    ROW ('b', 12)
    inverse 4
    step 8
    value 16
    ROW ('c', 16)
    inverse 5
    step 1
    value 12
    ROW ('d', 12)
    inverse 3
    value 9
    ROW ('e', 9)
    final 9


.. index:: Defining collations (sorting) (example code)

.. _example_collation:

Defining collations (sorting)
-----------------------------

How you sort can depend on the languages or values involved.  You
register a collation by calling :meth:`Connection.create_collation`.

.. code-block:: python

   # This example sorting mechanisms understands some text followed by a
   # number and ensures the number portion gets sorted correctly
   
   connection.execute("create table names(name)")
   connection.executemany(
       "insert into names values(?)",
       (
           ("file1",),
           ("file7",),
           ("file17",),
           ("file20",),
           ("file3",),
       ),
   )
   
   print("Standard sorting")
   for row in connection.execute("select * from names order by name"):
       print(row)
   
   
   def str_num_collate(
       s1: apsw.SQLiteValue, s2: apsw.SQLiteValue
   ) -> int:
       # return -1 if s1<s2, +1 if s1>s2 else 0 for equal
   
       def parts(s: str) -> list:
           "Converts str into list of alternating str and int parts"
           return [
               int(v) if v.isdigit() else v
               for v in re.split(r"(\d+)", s)
           ]
   
       ps1 = parts(str(s1))
       ps2 = parts(str(s2))
   
       # compare
       if ps1 < ps2:
           return -1
       if ps1 > ps2:
           return 1
       return 0
   
   
   connection.create_collation("strnum", str_num_collate)
   
   print("\nUsing strnum")
   for row in connection.execute(
       "select * from names order by name collate strnum"
   ):
       print(row)
   


.. code-block:: output

    Standard sorting
    ('file1',)
    ('file17',)
    ('file20',)
    ('file3',)
    ('file7',)
    
    Using strnum
    ('file1',)
    ('file3',)
    ('file7',)
    ('file17',)
    ('file20',)


.. index:: Accessing results by column name (example code)

.. _example_colnames:

Accessing results by column name
--------------------------------

You can access results by column name using :mod:`dataclasses`.
APSW provides :class:`apsw.ext.DataClassRowFactory` for names.

.. code-block:: python

   import apsw.ext
   
   connection.execute(
       """
       create table books(id, title, author, year);
       insert into books values(7, 'Animal Farm', 'George Orwell', 1945);
       insert into books values(37, 'The Picture of Dorian Gray', 'Oscar Wilde', 1890);
       """
   )
   
   # Normally you use column numbers
   for row in connection.execute(
       "select title, id, year from books where author=?",
       ("Oscar Wilde",),
   ):
       # this is very fragile
       print("title", row[0])
       print("id", row[1])
       print("year", row[2])
   
   # Turn on dataclasses - frozen makes them read-only
   connection.row_trace = apsw.ext.DataClassRowFactory(
       dataclass_kwargs={"frozen": True}
   )
   
   print("\nNow with dataclasses\n")
   
   # Same query - note using AS to set column name
   for row in connection.execute(
       """SELECT title,
              id AS book_id,
              year AS book_year
              FROM books WHERE author = ?""",
       ("Oscar Wilde",),
   ):
       print("title", row.title)
       print("id", row.book_id)
       print("year", row.book_year)
   
   # clear
   connection.row_trace = None
   


.. code-block:: output

    title The Picture of Dorian Gray
    id 37
    year 1890
    
    Now with dataclasses
    
    title The Picture of Dorian Gray
    id 37
    year 1890


.. index:: Type conversion into/out of database (example code)

.. _example_type_conversion:

Type conversion into/out of database
------------------------------------

You can use :class:`apsw.ext.TypesConverterCursorFactory` to do
conversion, both for types you define and for other types.

.. code-block:: python

   import apsw.ext
   
   registrar = apsw.ext.TypesConverterCursorFactory()
   connection.cursor_factory = registrar
   
   
   # A type we define - deriving from SQLiteTypeAdapter automatically registers conversion
   # to a SQLite value
   class Point(apsw.ext.SQLiteTypeAdapter):
       def __init__(self, x, y):
           self.x = x
           self.y = y
   
       def __repr__(self) -> str:
           return f"Point({ self.x }, { self.y })"
   
       def __eq__(self, other: object) -> bool:
           return (
               isinstance(other, type(self))
               and self.x == other.x
               and self.y == other.y
           )
   
       def to_sqlite_value(self) -> str:
           # called to convert Point into something SQLite supports
           return f"{ self.x };{ self.y }"
   
       # This converter will be registered
       @classmethod
       def convert_from_sqlite(cls, value: str) -> Point:
           return cls(*(float(part) for part in value.split(";")))
   
   
   # Existing types
   def complex_to_sqlite_value(c: complex) -> str:
       return f"{ c.real }+{ c.imag }"
   
   
   def datetime_to_sqlite_value(dt: datetime.datetime) -> float:
       # Represent as floating point UTC value no matter
       # what timezone is used. Also consider other
       # formats like ISO8601.
       return dt.timestamp()
   
   
   # ... require manual registration
   registrar.register_adapter(complex, complex_to_sqlite_value)
   registrar.register_adapter(datetime.datetime, datetime_to_sqlite_value)
   
   # conversion from a SQLite value requires registration
   registrar.register_converter("POINT", Point.convert_from_sqlite)
   
   
   # ... and for stdlib types
   def sqlite_to_complex(v: str) -> complex:
       return complex(*(float(part) for part in v.split("+")))
   
   
   def sqlite_to_datetime(v: float) -> datetime.datetime:
       # Keep the UTC values coming back from the database
       # as UTC
       return datetime.datetime.fromtimestamp(v, datetime.timezone.utc)
   
   
   registrar.register_converter("COMPLEX", sqlite_to_complex)
   registrar.register_converter("TIMESTAMP", sqlite_to_datetime)
   
   # note that the type names are case sensitive and must match the
   # registration
   connection.execute("create table conversion(p POINT, c COMPLEX, t TIMESTAMP)")
   
   # convert going into database
   test_data = (Point(5.2, 7.6), 3 + 4j, datetime.datetime.now())
   connection.execute("insert into conversion values(?, ?, ?)", test_data)
   print("inserted", test_data)
   
   # and coming back out
   print("querying data")
   for row in connection.execute("select * from conversion"):
       for i, value in enumerate(row):
           print(f"column {i} = { value !r}")
   
   # clear registrar
   connection.cursor_factory = apsw.Cursor
   


.. code-block:: output

    inserted (Point(5.2, 7.6), (3+4j), datetime.datetime(2024, 12, 8, 7, 15, 20, 138917))
    querying data
    column 0 = Point(5.2, 7.6)
    column 1 = (3+4j)
    column 2 = datetime.datetime(2024, 12, 8, 15, 15, 20, 138917, tzinfo=datetime.timezone.utc)


.. index:: Query details (example code)

.. _example_query_details:

Query details
-------------

:meth:`apsw.ext.query_info` can provide a lot of information about a
query (without running it)

.. code-block:: python

   import apsw.ext
   
   # test tables
   connection.execute(
       """
       create table customers(
           id INTEGER PRIMARY KEY,
           name CHAR,
           address CHAR);
       create table orders(
           id INTEGER PRIMARY KEY,
           customer_id INTEGER,
           item MY_OWN_TYPE);
       create index cust_addr on customers(address);
   """
   )
   
   query = """
       SELECT * FROM orders
       JOIN customers ON orders.customer_id=customers.id
       WHERE address = ?;
       SELECT 7;"""
   
   # ask for all information available
   qd = apsw.ext.query_info(
       connection,
       query,
       actions=True,  # which tables/views etc and how they are accessed
       explain=True,  # shows low level VDBE
       explain_query_plan=True,  # how SQLite solves the query
   )
   
   print("query", qd.query)
   print("\nbindings_count", qd.bindings_count)
   print("\nbindings_names", qd.bindings_names)
   print("\nexpanded_sql", qd.expanded_sql)
   print("\nfirst_query", qd.first_query)
   print("\nquery_remaining", qd.query_remaining)
   print("\nis_explain", qd.is_explain)
   print("\nis_readonly", qd.is_readonly)
   print("\ndescription")
   pprint(qd.description)
   if hasattr(qd, "description_full"):
       print("\ndescription_full")
       pprint(qd.description_full)
   
   print("\nquery_plan")
   pprint(qd.query_plan)
   print("\nFirst 5 actions")
   pprint(qd.actions[:5])
   print("\nFirst 5 explain")
   pprint(qd.explain[:5])
   


.. code-block:: output

    query 
        SELECT * FROM orders
        JOIN customers ON orders.customer_id=customers.id
        WHERE address = ?;
        SELECT 7;
    
    bindings_count 1
    
    bindings_names (None,)
    
    expanded_sql None
    
    first_query 
        SELECT * FROM orders
        JOIN customers ON orders.customer_id=customers.id
        WHERE address = ?;
        
    
    query_remaining SELECT 7;
    
    is_explain 0
    
    is_readonly True
    
    description
    (('id', 'INTEGER'),
     ('customer_id', 'INTEGER'),
     ('item', 'MY_OWN_TYPE'),
     ('id', 'INTEGER'),
     ('name', 'CHAR'),
     ('address', 'CHAR'))
    
    description_full
    (('id', 'INTEGER', 'main', 'orders', 'id'),
     ('customer_id', 'INTEGER', 'main', 'orders', 'customer_id'),
     ('item', 'MY_OWN_TYPE', 'main', 'orders', 'item'),
     ('id', 'INTEGER', 'main', 'customers', 'id'),
     ('name', 'CHAR', 'main', 'customers', 'name'),
     ('address', 'CHAR', 'main', 'customers', 'address'))
    
    query_plan
    QueryPlan(detail='QUERY PLAN',
              sub=[QueryPlan(detail='SCAN orders', sub=None),
                   QueryPlan(detail='SEARCH customers USING INTEGER PRIMARY KEY '
                                    '(rowid=?)',
                             sub=None)])
    
    First 5 actions
    [QueryAction(action=21,
                 action_name='SQLITE_SELECT',
                 column_name=None,
                 database_name=None,
                 file_name=None,
                 function_name=None,
                 module_name=None,
                 operation=None,
                 pragma_name=None,
                 pragma_value=None,
                 table_name=None,
                 trigger_name=None,
                 trigger_or_view=None,
                 view_name=None),
     QueryAction(action=20,
                 action_name='SQLITE_READ',
                 column_name='id',
                 database_name='main',
                 file_name=None,
                 function_name=None,
                 module_name=None,
                 operation=None,
                 pragma_name=None,
                 pragma_value=None,
                 table_name='orders',
                 trigger_name=None,
                 trigger_or_view=None,
                 view_name=None),
     QueryAction(action=20,
                 action_name='SQLITE_READ',
                 column_name='customer_id',
                 database_name='main',
                 file_name=None,
                 function_name=None,
                 module_name=None,
                 operation=None,
                 pragma_name=None,
                 pragma_value=None,
                 table_name='orders',
                 trigger_name=None,
                 trigger_or_view=None,
                 view_name=None),
     QueryAction(action=20,
                 action_name='SQLITE_READ',
                 column_name='item',
                 database_name='main',
                 file_name=None,
                 function_name=None,
                 module_name=None,
                 operation=None,
                 pragma_name=None,
                 pragma_value=None,
                 table_name='orders',
                 trigger_name=None,
                 trigger_or_view=None,
                 view_name=None),
     QueryAction(action=20,
                 action_name='SQLITE_READ',
                 column_name='id',
                 database_name='main',
                 file_name=None,
                 function_name=None,
                 module_name=None,
                 operation=None,
                 pragma_name=None,
                 pragma_value=None,
                 table_name='customers',
                 trigger_name=None,
                 trigger_or_view=None,
                 view_name=None)]
    
    First 5 explain
    [VDBEInstruction(addr=0,
                     opcode='Init',
                     comment=None,
                     p1=0,
                     p2=17,
                     p3=0,
                     p4=None,
                     p5=0),
     VDBEInstruction(addr=1,
                     opcode='OpenRead',
                     comment=None,
                     p1=0,
                     p2=12,
                     p3=0,
                     p4='3',
                     p5=0),
     VDBEInstruction(addr=2,
                     opcode='OpenRead',
                     comment=None,
                     p1=1,
                     p2=11,
                     p3=0,
                     p4='3',
                     p5=0),
     VDBEInstruction(addr=3,
                     opcode='Rewind',
                     comment=None,
                     p1=0,
                     p2=16,
                     p3=0,
                     p4=None,
                     p5=0),
     VDBEInstruction(addr=4,
                     opcode='Column',
                     comment=None,
                     p1=0,
                     p2=1,
                     p3=1,
                     p4=None,
                     p5=0)]


.. index:: Blob I/O (example code)

.. _example_blob_io:

Blob I/O
--------

BLOBS (binary large objects) are supported by SQLite.  Note that you
cannot change the size of one, but you can allocate one filled with
zeroes, and then later open it and read / write the contents similar
to a file, without having the entire blob in memory.  Use
:meth:`Connection.blob_open` to open a blob.

.. code-block:: python

   connection.execute("create table blobby(x,y)")
   # Add a blob we will fill in later
   connection.execute("insert into blobby values(1, zeroblob(10000))")
   # Or as a binding
   connection.execute(
       "insert into blobby values(2, ?)", (apsw.zeroblob(20000),)
   )
   # Open a blob for writing.  We need to know the rowid
   rowid = connection.execute("select ROWID from blobby where x=1").get
   blob = connection.blob_open("main", "blobby", "y", rowid, True)
   blob.write(b"hello world")
   blob.seek(2000)
   blob.read(24)
   # seek relative to the end
   blob.seek(-32, 2)
   blob.write(b"hello world, again")
   blob.close()
   

.. index:: Backup an open database (example code)

.. _example_backup:

Backup an open database
-----------------------

You can :ref:`backup <backup>` a database that is open.  The pages are copied in
batches of your choosing and allow continued use of the source
database.

.. code-block:: python

   # We will copy a disk database into this memory database
   destination = apsw.Connection(":memory:")
   
   # Copy into destination
   with destination.backup("main", connection, "main") as backup:
       # The source database can change while doing the backup
       # and the backup will still pick up those changes
       while not backup.done:
           backup.step(7)  # copy up to 7 pages each time
           # monitor progress
           print(backup.remaining, backup.page_count)
   
   


.. code-block:: output

    15 22
    8 22
    1 22
    0 22


.. index:: Authorizer (control what SQL can do) (example code)

.. _example_authorizer:

Authorizer (control what SQL can do)
------------------------------------

You can allow, deny, or ignore what SQL does.  Use
:attr:`Connection.authorizer` to set an authorizer.

.. code-block:: python

   
   def auth(
       operation: int,
       p1: Optional[str],
       p2: Optional[str],
       db_name: Optional[str],
       trigger_or_view: Optional[str],
   ) -> int:
       """Called when each operation is prepared.  We can return SQLITE_OK, SQLITE_DENY or
       SQLITE_IGNORE"""
       # find the operation name
       print(
           apsw.mapping_authorizer_function[operation],
           p1,
           p2,
           db_name,
           trigger_or_view,
       )
       if (
           operation == apsw.SQLITE_CREATE_TABLE
           and p1
           and p1.startswith("private")
       ):
           return apsw.SQLITE_DENY  # not allowed to create tables whose names start with private
   
       return apsw.SQLITE_OK  # always allow
   
   
   connection.authorizer = auth
   connection.execute("insert into names values('foo')")
   connection.execute("select name from names limit 1")
   try:
       connection.execute("create table private_stuff(secret)")
       print("Created secret table!")
   except Exception as e:
       print(e)
   
   # Clear authorizer
   connection.authorizer = None
   


.. code-block:: output

    SQLITE_INSERT names None main None
    SQLITE_SELECT None None None None
    SQLITE_READ names name main None
    SQLITE_INSERT sqlite_master None main None
    SQLITE_CREATE_TABLE private_stuff None main None
    not authorized


.. index:: Progress handler (example code)

.. _example_progress_handler:

Progress handler
----------------

Some operations (eg joins, sorting) can take many operations to
complete.  Register a progress handler callback with
:meth:`Connection.set_progress_handler` which lets you provide
feedback and allows cancelling.

.. code-block:: python

   # create a table with random numbers
   with connection:
       connection.execute("create table numbers(x)")
       connection.executemany(
           "insert into numbers values(?)",
           ((random.randint(0, 9999999999),) for _ in range(100)),
       )
   
   
   def progress_handler() -> bool:
       print("progress handler called")
       return False  # returning True aborts
   
   
   # register handler every 50 vdbe instructions
   connection.set_progress_handler(progress_handler, 50)
   
   # Sorting the numbers to find the biggest
   for max_num in connection.execute("select max(x) from numbers"):
       print(max_num)
   
   # Clear handler
   connection.set_progress_handler(None)
   


.. code-block:: output

    progress handler called
    progress handler called
    progress handler called
    progress handler called
    progress handler called
    progress handler called
    progress handler called
    progress handler called
    (9984270826,)


.. index:: File Control (example code)

.. _example_filecontrol:

File Control
------------

We can get/set low level information using the
:meth:`Connection.file_control` interface.  In this example we get
the `data version
<https://sqlite.org/c3ref/c_fcntl_begin_atomic_write.html#sqlitefcntldataversion>`__.
There is a `pragma
<https://sqlite.org/pragma.html#pragma_data_version>`__ but it
doesn't change for commits on the same connection.

.. code-block:: python

   # We use ctypes to provide the correct C level data types and pointers
   import ctypes
   
   
   def get_data_version(db):
       # unsigned 32 bit integer
       data_version = ctypes.c_uint32(0)
       ok = db.file_control(
           "main",  # or an attached database name
           apsw.SQLITE_FCNTL_DATA_VERSION,  # code
           ctypes.addressof(data_version),
       )  # pass C level pointer
       assert ok, "SQLITE_FCNTL_DATA_VERSION was not understood!"
       return data_version.value
   
   
   # Show starting values
   print(
       "fcntl",
       get_data_version(connection),
       "pragma",
       connection.pragma("data_version"),
   )
   
   # See the fcntl value versus pragma value
   for sql in (
       "create table fcntl_example(x)",
       "begin ; insert into fcntl_example values(3)",
       # we can see the version doesn't change inside a transaction
       "insert into fcntl_example values(4)",
       "commit",
       "pragma user_version=1234",
   ):
       print(sql)
       connection.execute(sql)
       print(
           "fcntl",
           get_data_version(connection),
           "pragma",
           connection.pragma("data_version"),
       )
   


.. code-block:: output

    fcntl 40 pragma 2
    create table fcntl_example(x)
    fcntl 41 pragma 2
    begin ; insert into fcntl_example values(3)
    fcntl 41 pragma 2
    insert into fcntl_example values(4)
    fcntl 41 pragma 2
    commit
    fcntl 42 pragma 2
    pragma user_version=1234
    fcntl 43 pragma 2


.. index:: Commit hook (example code)

.. _example_commit_hook:

Commit hook
-----------

A commit hook can allow or veto commits.  Register a commit hook
with  :meth:`Connection.set_commit_hook`.

.. code-block:: python

   
   def my_commit_hook() -> bool:
       print("in commit hook")
       hour = time.localtime()[3]
       if hour >= 8 and hour < 18:
           print("commits okay at this time")
           return False  # let commit go ahead
       print("no commits out of hours")
       return True  # abort commits outside of 8am through 6pm
   
   
   connection.set_commit_hook(my_commit_hook)
   try:
       with connection:
           connection.execute(
               """create table example(x,y,z);
                              insert into example values (3,4,5)"""
           )
   except apsw.ConstraintError:
       print("commit was not allowed")
   
   connection.set_commit_hook(None)
   


.. code-block:: output

    in commit hook
    no commits out of hours
    commit was not allowed


.. index:: Update hook (example code)

.. _example_update_hook:

Update hook
-----------

Update hooks let you know that data has been added, changed, or
removed.  For example you could use this to discard cached
information.  Register a hook using
:meth:`Connection.set_update_hook`.

.. code-block:: python

   
   def my_update_hook(
       type: int, db_name: str, table_name: str, rowid: int
   ) -> None:
       op: str = apsw.mapping_authorizer_function[type]
       print(
           f"Updated: { op } db { db_name }, table { table_name }, rowid { rowid }"
       )
   
   
   connection.set_update_hook(my_update_hook)
   connection.execute("insert into names values(?)", ("file93",))
   connection.execute(
       "update names set name=? where name=?", ("file94", "file93")
   )
   connection.execute("delete from names where name=?", ("file94",))
   
   # Clear the hook
   connection.set_update_hook(None)
   


.. code-block:: output

    Updated: SQLITE_INSERT db main, table names, rowid 7
    Updated: SQLITE_UPDATE db main, table names, rowid 7
    Updated: SQLITE_DELETE db main, table names, rowid 7


.. index:: Virtual tables (example code)

.. _example_virtual_tables:

Virtual tables
--------------

:ref:`Virtual tables <virtualtables>` let you provide data on demand
as a SQLite table so you can use SQL queries against that data.
Writing your own virtual table requires understanding how to return
less than all the data via the `BestIndex
<https://www.sqlite.org/vtab.html#the_xbestindex_method>`__ method.

You can export a Python function as a virtual table in 3 lines of
code using :func:`apsw.ext.make_virtual_module`, being able to
provide both positional and keyword arguments.

For the first example you'll find :meth:`apsw.ext.generate_series`
useful instead.

.. code-block:: python

   
   # Yield a row at a time
   def table_range(start=1, stop=100, step=1):
       for i in range(start, stop + 1, step):
           yield (i,)
   
   
   # set column names
   table_range.columns = ("value",)
   # set how to access what table_range returns
   table_range.column_access = apsw.ext.VTColumnAccess.By_Index
   
   # register it
   apsw.ext.make_virtual_module(connection, "range", table_range)
   
   # see it work.  we can provide both positional and keyword
   # arguments
   query = "SELECT * FROM range(90) WHERE step=2"
   print(apsw.ext.format_query_table(connection, query))
   
   # the parameters are hidden columns so '*' doesn't select them
   # but you can ask
   query = "SELECT *, start, stop, step FROM range(89) WHERE step=3"
   print(apsw.ext.format_query_table(connection, query))
   
   # Expose the unicode database.
   import unicodedata
   
   # A more complex example exporting unicodedata module
   
   # The methods we will call on each codepoint
   unicode_methods = (
       "name",
       "decimal",
       "digit",
       "numeric",
       "category",
       "combining",
       "bidirectional",
       "east_asian_width",
       "mirrored",
       "decomposition",
   )
   
   
   # the function we will turn into a virtual table returning
   # each row as a dict
   def unicode_data(start=0, stop=sys.maxunicode):
       # some methods raise ValueError on some codepoints
       def call(meth: str, c: str):
           try:
               return getattr(unicodedata, meth)(c)
           except ValueError:
               return None
   
       for c in range(start, stop + 1):
           yield {k: call(k, chr(c)) for k in unicode_methods}
   
   
   # setup column names and access
   unicode_data.columns = unicode_methods
   unicode_data.column_access = apsw.ext.VTColumnAccess.By_Name
   
   # register
   apsw.ext.make_virtual_module(connection, "unicode_data", unicode_data)
   
   # how many codepoints are in each category?
   query = """
       SELECT count(*), category FROM unicode_data
          WHERE stop = 0xffff  -- BMP only
          GROUP BY category
          ORDER BY category
          LIMIT 10"""
   print(apsw.ext.format_query_table(connection, query))
   
   
   # A more complex example - given a list of directories return information
   # about the files within them recursively
   def get_files_info(
       directories: str,
       sep: str = os.pathsep,
       *,
       ignore_symlinks: bool = True,
   ) -> Iterator[dict[str, Any]]:
       for root in directories.split(sep):
           with os.scandir(root) as sd:
               for entry in sd:
                   if entry.is_symlink() and ignore_symlinks:
                       continue
                   if entry.is_dir():
                       yield from get_files_info(
                           os.path.join(root, entry.name),
                           ignore_symlinks=ignore_symlinks,
                       )
                   elif entry.is_file():
                       s = entry.stat()
                       yield {
                           "directory": root,
                           "name": entry.name,
                           "extension": os.path.splitext(entry.name)[1],
                           **{k: getattr(s, k) for k in get_files_info.stat_columns},
                       }
   
   
   # which stat columns do we want?
   get_files_info.stat_columns = tuple(
       n for n in dir(os.stat(".")) if n.startswith("st_")
   )
   # setup columns and access by providing an example of the first entry returned
   (
       get_files_info.columns,
       get_files_info.column_access,
   ) = apsw.ext.get_column_names(next(get_files_info(".")))
   
   apsw.ext.make_virtual_module(connection, "files_info", get_files_info)
   
   # all the sys.path directories
   bindings = (
       os.pathsep.join(
           p
           for p in sys.path
           if os.path.isdir(p)
           #  except our current one
           and not os.path.samefile(p, ".")
       ),
   )
   
   # Find the 3 biggest files that aren't libraries
   query = """SELECT st_size, directory, name
               FROM files_info(?)
               WHERE extension NOT IN ('.a', '.so')
               ORDER BY st_size DESC
               LIMIT 3"""
   print(apsw.ext.format_query_table(connection, query, bindings))
   
   # Find the 3 oldest Python files
   query = """SELECT DATE(st_ctime, 'auto') AS date, directory, name
               FROM files_info(?)
               WHERE extension='.py'
               ORDER BY st_size DESC
               LIMIT 3"""
   print(apsw.ext.format_query_table(connection, query, bindings))
   
   # find space used by filename extension
   query = """SELECT extension, SUM(st_size) as total_size
               FROM files_info(?)
               GROUP BY extension
               ORDER BY extension"""
   print(apsw.ext.format_query_table(connection, query, bindings))
   
   # unregister a virtual table by passing None
   connection.create_module("files_info", None)
   


.. code-block:: output

    ┌───────┐
    │ value │
    │ 90    │
    │ 92    │
    │ 94    │
    │ 96    │
    │ 98    │
    │ 100   │
    └───────┘
    
    ┌───────┬───────┬──────┬──────┐
    │ value │ start │ stop │ step │
    │ 89    │ 89    │ 100  │ 3    │
    │ 92    │ 89    │ 100  │ 3    │
    │ 95    │ 89    │ 100  │ 3    │
    │ 98    │ 89    │ 100  │ 3    │
    └───────┴───────┴──────┴──────┘
    
    ┌──────────┬──────────┐
    │ count(*) │ category │
    │ 65       │ Cc       │
    │ 43       │ Cf       │
    │ 1454     │ Cn       │
    │ 6400     │ Co       │
    │ 2048     │ Cs       │
    │ 1445     │ Ll       │
    │ 236      │ Lm       │
    │ 46126    │ Lo       │
    │ 31       │ Lt       │
    │ 1127     │ Lu       │
    └──────────┴──────────┘
    
    ┌─────────┬──────────────────────────────────────────┬─────────────────────────┐
    │ st_size │                directory                 │          name           │
    ├─────────┼──────────────────────────────────────────┼─────────────────────────┤
    │ 815083  │ /usr/lib/python3.12/pydoc_data           │ topics.py               │
    ├─────────┼──────────────────────────────────────────┼─────────────────────────┤
    │ 509199  │ /usr/lib/python3.12/pydoc_data/          │ topics.cpython-312.pyc  │
    │         │ __pycache__                              │                         │
    ├─────────┼──────────────────────────────────────────┼─────────────────────────┤
    │ 245940  │ /usr/lib/python3.12/tkinter/__pycache__  │ __init__.cpython-312.p- │
    │         │                                          │ yc                      │
    └─────────┴──────────────────────────────────────────┴─────────────────────────┘
    
    ┌────────────┬────────────────────────────────┬───────────────┐
    │    date    │           directory            │     name      │
    │ 2024-11-20 │ /usr/lib/python3.12/pydoc_data │ topics.py     │
    │ 2024-11-20 │ /usr/lib/python3.12            │ _pydecimal.py │
    │ 2024-11-20 │ /usr/lib/python3.12/tkinter    │ __init__.py   │
    └────────────┴────────────────────────────────┴───────────────┘
    
    ┌────────────┬────────────┐
    │ extension  │ total_size │
    │            │ 436917     │
    │ .a         │ 97341326   │
    │ .allowlist │ 72         │
    │ .bootstrap │ 1804       │
    │ .c         │ 10948      │
    │ .cfg       │ 341        │
    │ .csh       │ 934        │
    │ .css       │ 1325       │
    │ .fish      │ 2209       │
    │ .in        │ 3504       │
    │ .ini       │ 997        │
    │ .json      │ 2162       │
    │ .local     │ 2136       │
    │ .o         │ 9360       │
    │ .ps1       │ 9033       │
    │ .py        │ 11255420   │
    │ .pyc       │ 11434843   │
    │ .rst       │ 9561       │
    │ .sh        │ 2652       │
    │ .so        │ 26583216   │
    │ .sql       │ 1001       │
    │ .stdlib    │ 12562      │
    │ .supp      │ 70         │
    │ .txt       │ 13936      │
    └────────────┴────────────┘
    


.. index:: VFS - Virtual File System (example code)

.. _example_vfs:

VFS - Virtual File System
-------------------------

:ref:`VFS <vfs>` lets you control how SQLite accesses storage.  APSW
makes it easy to "inherit" from an existing VFS and monitor or alter
data as it flows through.

:class:`URI <URIFilename>` are shown as a way to receive parameters
when opening/creating a database file, and :class:`pragmas <VFSFcntlPragma>`
for receiving parameters once a database is open.

.. code-block:: python

   # This example VFS obfuscates the database file contents by xor all
   # bytes with 0xa5.
   
   
   def obfuscate(data: bytes):
       return bytes([x ^ 0xA5 for x in data])
   
   
   # Inheriting from a base of "" means the default vfs
   class ObfuscatedVFS(apsw.VFS):
       def __init__(self, vfsname="obfuscated", basevfs=""):
           self.vfs_name = vfsname
           self.base_vfs = basevfs
           super().__init__(self.vfs_name, self.base_vfs)
   
       # We want to return our own file implementation, but also
       # want it to inherit
       def xOpen(self, name, flags):
           in_flags = []
           for k, v in apsw.mapping_open_flags.items():
               if isinstance(k, int) and flags[0] & k:
                   in_flags.append(v)
           print("xOpen flags", " | ".join(in_flags))
   
           if isinstance(name, apsw.URIFilename):
               print("   uri filename", name.filename())
               # We can look at uri parameters
               print("   fast is", name.uri_parameter("fast"))
               print("   level is", name.uri_int("level", 3))
               print("   warp is", name.uri_boolean("warp", False))
               print(
                   "   notpresent is", name.uri_parameter("notpresent")
               )
               # all of them
               print("   all uris", name.parameters)
           else:
               print("   filename", name)
           return ObfuscatedVFSFile(self.base_vfs, name, flags)
   
   
   # The file implementation where we override xRead and xWrite to call our
   # encryption routine
   class ObfuscatedVFSFile(apsw.VFSFile):
       def __init__(self, inheritfromvfsname, filename, flags):
           super().__init__(inheritfromvfsname, filename, flags)
   
       def xRead(self, amount, offset):
           return obfuscate(super().xRead(amount, offset))
   
       def xWrite(self, data, offset):
           super().xWrite(obfuscate(data), offset)
   
       def xFileControl(self, op: int, ptr: int) -> bool:
           if op != apsw.SQLITE_FCNTL_PRAGMA:
               return super().xFileControl(op, ptr)
           # implement our own pragma
           p = apsw.VFSFcntlPragma(ptr)
           print(f"pragma received { p.name } = { p.value }")
           # what do we understand?
           if p.name == "my_custom_pragma":
               p.result = "orange"
               return True
           # We did not understand
           return False
   
   
   # To register the VFS we just instantiate it
   obfuvfs = ObfuscatedVFS()
   
   # Lets see what vfs are now available?
   print("VFS available", apsw.vfs_names())
   
   # Make an obfuscated db, passing in some URI parameters
   # default open flags
   open_flags = apsw.SQLITE_OPEN_READWRITE | apsw.SQLITE_OPEN_CREATE
   # add in using URI parameters
   open_flags |= apsw.SQLITE_OPEN_URI
   
   # uri parameters are after the ? separated by &
   obfudb = apsw.Connection(
       "file:myobfudb?fast=speed&level=7&warp=on&another=true",
       flags=open_flags,
       vfs=obfuvfs.vfs_name,
   )
   
   # Check it works
   obfudb.execute("create table foo(x,y); insert into foo values(1,2)")
   
   # Check it really is obfuscated on disk
   print("What is on disk", repr(Path("myobfudb").read_bytes()[:20]))
   
   # And unobfuscating it
   print(
       "Unobfuscated disk",
       repr(obfuscate(Path("myobfudb").read_bytes()[:20])),
   )
   
   # Custom pragma
   print(
       "pragma returned", obfudb.pragma("my_custom_pragma", "my value")
   )
   
   # Tidy up
   obfudb.close()
   os.remove("myobfudb")
   


.. code-block:: output

    VFS available ['unix', 'obfuscated', 'memdb', 'unix-excl', 'unix-dotfile', 'unix-none']
    xOpen flags SQLITE_OPEN_CREATE | SQLITE_OPEN_MAIN_DB | SQLITE_OPEN_READWRITE | SQLITE_OPEN_URI
       uri filename /space/apsw/myobfudb
       fast is speed
       level is 7
       warp is True
       notpresent is None
       all uris ('fast', 'level', 'warp', 'another')
    pragma received journal_mode = wal
    xOpen flags SQLITE_OPEN_CREATE | SQLITE_OPEN_MAIN_JOURNAL | SQLITE_OPEN_READWRITE
       filename /space/apsw/myobfudb-journal
    pragma received foreign_keys = ON
    pragma received optimize = 65538
    xOpen flags SQLITE_OPEN_CREATE | SQLITE_OPEN_READWRITE | SQLITE_OPEN_WAL
       filename /space/apsw/myobfudb-wal
    pragma received recursive_triggers = ON
    What is on disk b'\xf6\xf4\xe9\xcc\xd1\xc0\x85\xc3\xca\xd7\xc8\xc4\xd1\x85\x96\xa5\xb5\xa5\xa7\xa7'
    Unobfuscated disk b'SQLite format 3\x00\x10\x00\x02\x02'
    pragma received my_custom_pragma = my value
    pragma returned orange


.. index:: Limits (example code)

.. _example_limits:

Limits
------

SQLite lets you see and update various limits via
:meth:`Connection.limit`

.. code-block:: python

   # Print some limits
   for limit in ("LENGTH", "COLUMN", "ATTACHED"):
       name = "SQLITE_LIMIT_" + limit
       max_name = "SQLITE_MAX_" + limit  # compile time limit
       orig = connection.limit(getattr(apsw, name))
       print(name, orig)
       # To get the maximum, set to 0x7fffffff and then read value back
       connection.limit(getattr(apsw, name), 0x7FFFFFFF)
       max = connection.limit(getattr(apsw, name))
       print(max_name, " ", max)
   
   # Set limit for size of a string
   connection.execute("create table testlimit(s)")
   connection.execute(
       "insert into testlimit values(?)", ("x" * 1024,)
   )  # 1024 char string
   connection.limit(apsw.SQLITE_LIMIT_LENGTH, 1023)  # limit is now 1023
   try:
       connection.execute(
           "insert into testlimit values(?)", ("y" * 1024,)
       )
       print("string exceeding limit was inserted")
   except apsw.TooBigError:
       print("Caught toobig exception")
   
   # reset back to largest value
   connection.limit(apsw.SQLITE_LIMIT_LENGTH, 0x7FFFFFFF)
   


.. code-block:: output

    SQLITE_LIMIT_LENGTH 1000000000
    SQLITE_MAX_LENGTH   1000000000
    SQLITE_LIMIT_COLUMN 2000
    SQLITE_MAX_COLUMN   2000
    SQLITE_LIMIT_ATTACHED 125
    SQLITE_MAX_ATTACHED   125
    Caught toobig exception


.. index:: Shell (example code)

.. _example_shell:

Shell
-----

APSW includes a :ref:`shell <shell>`  like the one in `SQLite
<https://sqlite.org/cli.html>`__, and is also extensible from
Python.

.. code-block:: python

   import apsw.shell
   
   # Here we use the shell to do a csv export and then dump part of the
   # database
   
   # Export to a StringIO
   import io
   
   output = io.StringIO()
   shell = apsw.shell.Shell(stdout=output, db=connection)
   
   # How to execute a dot command
   shell.process_command(".mode csv")
   shell.process_command(".headers on")
   
   # How to execute SQL
   shell.process_sql(
       """
       create table csvtest(column1, column2 INTEGER);
       create index faster on csvtest(column1);
       insert into csvtest values(3, 4);
       insert into csvtest values('a b', NULL);
   """
   )
   
   # Or let the shell figure out SQL vs dot command
   shell.process_complete_line("select * from csvtest")
   
   # see the result
   print(output.getvalue())
   
   # reset output
   output.seek(0)
   
   # make a dump of the same table
   shell.process_command(".dump csvtest%")
   
   # see the result
   print("\nDump output\n")
   print(output.getvalue())
   


.. code-block:: output

    column1,column2
    3,4
    a b,
    
    
    Dump output
    
    -- SQLite dump (by APSW 3.47.2.0)
    -- SQLite version 3.47.2
    -- Date: Sun Dec  8 07:15:20 2024
    -- Tables like: csvtest%
    -- Database: /space/apsw/dbfile
    -- User: rogerb @ clamps
    
    -- The values of various per-database settings
    PRAGMA page_size=4096;
    -- PRAGMA encoding='UTF-8';
    -- PRAGMA auto_vacuum=NONE;
    -- PRAGMA max_page_count=4294967294;
    
    BEGIN TRANSACTION;
    
    -- Table  csvtest
    DROP TABLE IF EXISTS csvtest;
    CREATE TABLE csvtest(column1, column2 INTEGER);
    INSERT INTO csvtest VALUES(3,4);
    INSERT INTO csvtest VALUES('a b',NULL);
    -- Triggers and indices on  csvtest
    CREATE INDEX faster on csvtest(column1);
    
    -- Database header
    pragma user_version=1234;
    
    COMMIT TRANSACTION;
    


.. index:: Statistics (example code)

.. _example_status:

Statistics
----------

SQLite provides statistics by :meth:`status`.  Use :meth:`Connection.status`
for per connection statistics.

.. code-block:: python

   current_usage, max_usage = apsw.status(apsw.SQLITE_STATUS_MEMORY_USED)
   print(f"SQLite memory usage { current_usage } max { max_usage }")
   schema_used, _ = connection.status(apsw.SQLITE_DBSTATUS_SCHEMA_USED)
   print(
       f"{ schema_used } bytes used to store schema for this connection"
   )
   


.. code-block:: output

    SQLite memory usage 509184 max 2491056
    4680 bytes used to store schema for this connection


.. index:: Tracing (example code)

.. _example_trace_v2:

Tracing
-------

This shows using :meth:`Connection.trace_v2`

.. code-block:: python

   # From https://www.sqlite.org/lang_with.html
   # Outlandish Recursive Query Examples
   
   query = """WITH RECURSIVE
               xaxis(x) AS (VALUES(-2.0) UNION ALL SELECT x+0.05 FROM xaxis WHERE x<1.2),
               yaxis(y) AS (VALUES(-1.0) UNION ALL SELECT y+0.1 FROM yaxis WHERE y<1.0),
               m(iter, cx, cy, x, y) AS (
                   SELECT 0, x, y, 0.0, 0.0 FROM xaxis, yaxis
                   UNION ALL
                   SELECT iter+1, cx, cy, x*x-y*y + cx, 2.0*x*y + cy FROM m
                   WHERE (x*x + y*y) < 4.0 AND iter<28
               ),
               m2(iter, cx, cy) AS (
                   SELECT max(iter), cx, cy FROM m GROUP BY cx, cy
               ),
               a(t) AS (
                   SELECT group_concat( substr(' .+*#', 1+min(iter/7,4), 1), '')
                   FROM m2 GROUP BY cy
               )
               SELECT group_concat(rtrim(t),x'0a') FROM a;"""
   
   
   def trace_hook(trace: dict) -> None:
       # check the sql and connection are as expected and remove from trace
       # so we don't print them
       assert (
           trace.pop("sql", query) == query
           and trace.pop("connection") is connection
       )
       print("code is ", apsw.mapping_trace_codes[trace["code"]])
       pprint(trace)
   
   
   connection.trace_v2(
       apsw.SQLITE_TRACE_STMT
       | apsw.SQLITE_TRACE_PROFILE
       | apsw.SQLITE_TRACE_ROW,
       trace_hook,
   )
   
   # We will get one each of the trace events
   for _ in connection.execute(query):
       pass
   
   # Turn off tracing
   connection.trace_v2(0, None)
   


.. code-block:: output

    code is  SQLITE_TRACE_STMT
    {'code': 1, 'id': 385403960, 'total_changes': 146, 'trigger': False}
    code is  SQLITE_TRACE_ROW
    {'code': 4, 'id': 385403960}
    code is  SQLITE_TRACE_PROFILE
    {'code': 2,
     'id': 385403960,
     'nanoseconds': 17000000,
     'stmt_status': {'SQLITE_STMTSTATUS_AUTOINDEX': 0,
                     'SQLITE_STMTSTATUS_FILTER_HIT': 0,
                     'SQLITE_STMTSTATUS_FILTER_MISS': 0,
                     'SQLITE_STMTSTATUS_FULLSCAN_STEP': 1365,
                     'SQLITE_STMTSTATUS_MEMUSED': 15784,
                     'SQLITE_STMTSTATUS_REPREPARE': 0,
                     'SQLITE_STMTSTATUS_RUN': 1,
                     'SQLITE_STMTSTATUS_SORT': 2,
                     'SQLITE_STMTSTATUS_VM_STEP': 1015351},
     'total_changes': 146}


.. index:: System and SQLite resource usage in a block (example code)

.. _example_ShowResourceUsage:

System and SQLite resource usage in a block
-------------------------------------------

Use :meth:`apsw.ext.ShowResourceUsage` to see what resources a
block of code does.  We use the same query from above.

Only statistics that have changed are shown in the summary. There are
20 SQLite values tracked including caching, and 20 system values.

.. code-block:: python

   with apsw.ext.ShowResourceUsage(
       sys.stdout, db=connection, scope="thread"
   ):
       # some SQLite work
       rows = connection.execute(query).get
       # and some non-SQLite work - the imports cause filesystem access
       import statistics, tokenize, uuid, fractions, pydoc, decimal
   
       # and take some wall clock time
       time.sleep(1.3)
   


.. code-block:: output

                           Total CPU consumption 0.020
                                      Wall clock 1.324
                          Block input operations 176
                       Maximum resident set size 768
                            Page faults - no I/O 166
                    Involuntary context switches 4
                      Voluntary context switches 3
                               Time in user mode 0.019
                          SQLite full table scan 1,365
                          SQLite sort operations 2
                            SQLite vm operations 1,015,351
                     SQLite statements completed 1
               SQLite allocations lookaside full 17,272
    


.. index:: SQL statement tracing in a block (example code)

.. _example_Trace:

SQL statement tracing in a block
--------------------------------

Use :meth:`apsw.ext.Trace` to see SQL statements inside a block of
code.  This also shows behind the scenes SQL.

.. code-block:: python

   # Use None instead of stdout and no information is printed or gathered
   with apsw.ext.Trace(sys.stdout, db=connection, vtable=True):
   
       # APSW does a savepoint behind the scenes to wrap the block
       with connection:
           # Some regular SQL
           connection.execute("create table multi(x)")
           # executemany runs the same statement repeatedly
           connection.executemany("insert into multi values(?)", ((x,) for x in range(5)))
           # See how many rows were processed
           connection.execute("select * from multi limit 2").fetchall()
           # You can also see how many rows were changed
           connection.execute("delete from multi where x < 4")
           # To implement the table, SQLIte issues the pragma behind the
           # scenes.  Note how the output shows this statement starting,
           # the pragma, and then this statement ending.
           connection.execute("select count(*) from pragma_function_list")
   


.. code-block:: output

     > SAVEPOINT "_apsw-0"
         Time: 0.000
     > create table multi(x)
         Time: 0.000
     > insert into multi values(?)
         Time: 0.000  Rows: 1  Changes: 1
     > insert into multi values(?)
         Time: 0.000  Changes: 1
     > insert into multi values(?)
         Time: 0.000  Changes: 1
     > insert into multi values(?)
         Time: 0.000  Changes: 1
     > insert into multi values(?)
         Time: 0.000  Changes: 1
     > select * from multi limit 2
         Time: 0.000  Rows: 2
     > delete from multi where x < 4
         Time: 0.000  Changes: 4
     > select count(*) from pragma_function_list
     V PRAGMA function_list
         Time: 0.000  Rows: 206  VmStep: 1,446  Mem: 70.7KB
     < select count(*) from pragma_function_list
         Time: 0.000  Rows: 1  VmStep: 423
     > RELEASE SAVEPOINT "_apsw-0"
         Time: 0.007
    


.. index:: Formatting query results table (example code)

.. _example_format_query:

Formatting query results table
------------------------------

:meth:`apsw.ext.format_query_table` makes it easy
to format the results of a query in an automatic
adjusting table, colour, sanitizing strings,
truncation etc.

.. code-block:: python

   # Create a table with some dummy data
   connection.execute(
       """CREATE TABLE dummy(quantity, [spaces in name], last);
       INSERT INTO dummy VALUES(3, 'some regular text to make this row interesting', x'030709');
       INSERT INTO dummy VALUES(3.14, 'Tiếng Việt', null);
       INSERT INTO dummy VALUES('', ?, ' ');
   """,
       ("special \t\n\f\0 cha\\rs",),
   )
   
   query = "SELECT * FROM dummy"
   # default
   print(apsw.ext.format_query_table(connection, query))
   
   # no unicode boxes and maximum sanitize the text
   kwargs = {"use_unicode": False, "string_sanitize": 2}
   print(apsw.ext.format_query_table(connection, query, **kwargs))
   
   # lets have unicode boxes and make things narrow
   kwargs = {
       "use_unicode": True,
       "string_sanitize": 0,
       "text_width": 30,
   }
   print(apsw.ext.format_query_table(connection, query, **kwargs))
   
   # have the values in SQL syntax
   kwargs = {"quote": True}
   print(apsw.ext.format_query_table(connection, query, **kwargs))
   


.. code-block:: output

    ┌──────────┬────────────────────────────────────────────────┬─────────────┐
    │ quantity │                 spaces in name                 │    last     │
    ├──────────┼────────────────────────────────────────────────┼─────────────┤
    │ 3        │ some regular text to make this row interesting │ [ 3 bytes ] │
    ├──────────┼────────────────────────────────────────────────┼─────────────┤
    │ 3.14     │ Tiếng Việt                                     │ (null)      │
    ├──────────┼────────────────────────────────────────────────┼─────────────┤
    │          │ special                                        │             │
    │          │ \0 cha\\rs                                     │             │
    └──────────┴────────────────────────────────────────────────┴─────────────┘
    
    +----------+------------------------------------------------+-------------+
    | quantity |                 spaces in name                 |    last     |
    +----------+------------------------------------------------+-------------+
    | 3        | some.regular.text.to.make.this.row.interesting | [ 3 bytes ] |
    +----------+------------------------------------------------+-------------+
    | 3.14     | Ti.ng.Vi.t                                     | (null)      |
    +----------+------------------------------------------------+-------------+
    |          | special..                                      | .           |
    |          | ...cha\rs                                      |             |
    +----------+------------------------------------------------+-------------+
    
    ┌─────┬────────────────┬─────┐
    │ qu- │ spaces in name │ la- │
    │ an- │                │ st  │
    │ ti- │                │     │
    │ ty  │                │     │
    ├─────┼────────────────┼─────┤
    │ 3   │ some regular   │ [ 3 │
    │     │ text to make   │ by- │
    │     │ this row       │ te- │
    │     │ interesting    │ s ] │
    ├─────┼────────────────┼─────┤
    │ 3.- │ Tiếng Việt     │ (n- │
    │ 14  │                │ ul- │
    │     │                │ l)  │
    ├─────┼────────────────┼─────┤
    │     │ special        │     │
    │     │ \0 cha\\rs     │     │
    └─────┴────────────────┴─────┘
    
    ┌──────────┬──────────────────────────────────────────────────┬───────────┐
    │ quantity │                  spaces in name                  │   last    │
    ├──────────┼──────────────────────────────────────────────────┼───────────┤
    │ 3        │ 'some regular text to make this row interesting' │ X'030709' │
    ├──────────┼──────────────────────────────────────────────────┼───────────┤
    │ 3.14     │ 'Tiếng Việt'                                     │ NULL      │
    ├──────────┼──────────────────────────────────────────────────┼───────────┤
    │ ''       │ 'special                                         │ ' '       │
    │          │ \0 cha\\rs'                                      │           │
    └──────────┴──────────────────────────────────────────────────┴───────────┘
    


.. index:: Cleanup (example code)

.. _example_cleanup:

Cleanup
-------

As a general rule you do not need to do any cleanup.  Standard
Python garbage collection will take of everything.  Even if the
process crashes with a connection in the middle of a transaction,
the next time SQLite opens that database it will automatically
rollback the incomplete transaction.

.. code-block:: python

   # You can close connections manually
   connection.close()
