<title>SQLite Changes From Version 3.5.9 To 3.6.0</title>
<tcl>
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hd_keywords *35to36
HEADING 0 {Moving From SQLite 3.5.9 to 3.6.0}

PARAGRAPH {
  SQLite version 3.6.0 ([dateof:3.6.0])
  contains many changes.  As is the custom with
  the SQLite project, most changes are fully backwards compatible.
  However, a few of the changes in version 3.6.0 are incompatible and
  might require modifications to application code and/or makefiles.
  This document is a briefing on the changes in SQLite 3.6.0
  with special attention to the incompatible changes.
}

INDENTED {
  <strong>Key Points:</strong>
  <ul>
  <li> The database file format is unchanged. </li>
  <li> All incompatibilities are on obscure interfaces and hence should
       have zero impact on most applications. </li>
  </ul>
}

HEADING 1 {Incompatible Changes}

PARAGRAPH {
  Incompatible changes are covered first since they are the most
  important to maintainers and programmers.
}
HEADING 2 {Overview Of Incompatible Changes}

PARAGRAPH {
  <ol>
  <li><p>Changes to the [sqlite3_vfs] object</p>

      <ol type="a">
      <li><p>The signature of the xAccess method has been modified to
      return an [error code] and to store its output into an integer pointed
      to by a parameter, rather than returning the output directly.
      This change allows the xAccess() method to report failures.
      In association with this signature change, a new 
      extended error code [SQLITE_IOERR_ACCESS] has been added.
      </p></li>

      <li><p>The xGetTempname method has been removed from [sqlite3_vfs].
      In its place, the xOpen method is enhanced to open a temporary file
      of its own invention when the filename parameter is NULL.</p></li>

      <li><p>Added the xGetLastError() method to [sqlite3_vfs] for returning
      filesystem-specific error messages and error codes back to
      SQLite.</p></li>
      </ol>
  </li>

  <li><p>The signature of the xCheckReservedLock method on [sqlite3_io_methods]
      has been modified so that it returns an [error code] and stores its
      boolean result into an integer pointed to by a parameter.  In
      association with this change, a new extended error code
      [SQLITE_IOERR_CHECKRESERVEDLOCK] has been added.</p></li>

  <li><p>When SQLite is ported to new operating systems (operating systems 
      other than Unix, Windows, and OS/2 for which ports are provided together
      with the core)
      two new functions, [sqlite3_os_init()] and [sqlite3_os_end()], must
      be provided as part of the port.</p></li>

  <li><p>The way in which the IN and NOT IN operators handle NULL values
      in their right-hand expressions has been brought into compliance with
      the SQL standard and with other SQL database engines.</p></li>

  <li><p>The column names for the result sets of [SELECT] statements have
      been tweaked in some cases to work more like other SQL database
      engines.</p></li>      

  <li><p>Changes to compile-time options:</p>

      <ol type="a">
      <li><p>The SQLITE_MUTEX_APPDEF compile-time parameter is no longer
      recognized.  As a replacement, alternative 
      [sqlite3_mutex_enter | mutex implementations] may be created
      at runtime using [sqlite3_config()] with the [SQLITE_CONFIG_MUTEX]
      operator and the [sqlite3_mutex_methods] object.</p></li>

      <li><p>Compile-time options OS_UNIX, OS_WIN, OS_OS2, OS_OTHER, and
      TEMP_STORE have been renamed to include an "SQLITE_" prefix in order
      to help avoid namespace collisions with application software.  The
      new names of these options are respectively:
      SQLITE_OS_UNIX, SQLITE_OS_WIN, SQLITE_OS_OS2, SQLITE_OS_OTHER,
      and [SQLITE_TEMP_STORE].</p></li>
      </ol>
  </li>
  </ol>
}

HEADING 2 {Changes To The VFS Layer}

PARAGRAPH {
  SQLite [version 3.5.0] introduced a [34to35 | new OS interface layer] that
  provided an abstraction of the underlying operating system.
  This was an important innovation and has proven to be helpful
  in porting and maintaining SQLite.
  However, the developers have discovered some minor flaws in the
  original "virtual file system" design introduced in version 3.5.0
  and so SQLite 3.6.0 includes some small incompatible changes
  to address these flaws.
}

INDENTED {
  <strong>Key Point:</strong>  The incompatible
  changes in the SQLite operating-system interface for version 3.6.0
  only affect the rare applications that make use of the 
  [sqlite3_vfs | virtual file system] interface or that
  supply an application-defined [sqlite3_mutex_enter | mutex implementation]
  or that make use of other obscure compile-time options.  The
  changes introduced by SQLite version 3.6.0 will have zero impact on the
  vast majority of SQLite applications that use the built-in interfaces
  to Unix, Windows, and OS/2 and that use the standard build configuration.
}

HEADING 2 {Changes In The Way The IN Operator Handles NULLs}

PARAGRAPH {
  All versions of SQLite up to and including version 3.5.9 have mishandled
  NULL values on the right-hand side of IN and NOT IN operators.
  Specifically, SQLite has previously ignored NULLs on the right-hand side
  of IN and NOT IN.
}

PARAGRAPH {
  Suppose we have a table X1 defined as follows:
}

CODE {
  CREATE TABLE x1(x INTEGER);
  INSERT INTO x1 VALUES(1);
  INSERT INTO x1 VALUES(2);
  INSERT INTO x1 VALUES(NULL);
}

PARAGRAPH {
  Given the definition of X1 above, the following expressions have
  historically evaluated to FALSE in SQLite, though the correct
  answer is actually NULL:
}

CODE {
  3 IN (1,2,NULL)
  3 IN (SELECT * FROM x1)
}

PARAGRAPH {
  Similarly, the following expressions have historically evaluated to
  TRUE when in fact NULL is also the correct answer here:
}

CODE {
  3 NOT IN (1,2,NULL)
  3 NOT IN (SELECT * FROM x1)
}

PARAGRAPH {
  The historical behavior of SQLite is incorrect according to the SQL:1999
  standard and it is inconsistent with the behavior of MySQL and
  PostgreSQL.  Version 3.6.0 changes the behavior of the IN and
  NOT IN operators to conform to the standard and to give the same
  results as other SQL database engines.
}

INDENTED {
  <strong>Key Point:</strong> The change to the way NULL values are handled
  by the IN and NOT IN operators is technically a bug fix, not a design
  change.  However, maintainers should check to ensure that applications
  do not depend on the older, buggy behavior prior to upgrading to
  version 3.6.0.
}

HEADING 2 {Changes To Column Naming Rules}

PARAGRAPH {
  The column names reported by join subqueries have been modified slightly
  in order to work more like other database engines.  Consider the following
  query:
}

CODE {
  CREATE TABLE t1(a);
  CREATE TABLE t2(x);
  SELECT * FROM (SELECT t1.a FROM t1 JOIN t2 ORDER BY t2.x LIMIT 1) ORDER BY 1;
}

PARAGRAPH {
  In version 3.5.9 the query above would return a single column named "t1.a".
  In version 3.6.0 the column name is just "a".
}

PARAGRAPH {
  SQLite has never made any promises about the names of columns in the
  result set of [SELECT] statement unless the column contains an AS clause.
  So this change to column name is technically not an incompatibility.
  SQLite is merely changing from one undefined behavior to another.
  Nevertheless, many applications depend on the unspecified column naming
  behavior of SQLite and so this change is discussed under the
  incompatible changes subheading.
}
  
HEADING 2 {Changes To Compile-Time Options}

PARAGRAPH {
  Compile-time options to SQLite are controlled by C-preprocessor 
  macros.  SQLite version 3.6.0 changes the names of some of these
  macros so that all C-preprocessor macros that are specific to
  SQLite begin with the "SQLITE_" prefix.  This is done to reduce the
  risk of name collisions with other software modules.
}

INDENTED {
  <strong>Key Point:</strong>  Changes to compile-time options have the
  potential to affect makefiles in projects that do customized builds of
  SQLite. These changes should have zero impact on application code and for
  most projects which use a standard, default build of SQLite.
}


HEADING 1 {Fully Backwards-Compatible Enhancements}

PARAGRAPH {
  In addition to the incompatible changes listed above, SQLite
  version 3.6.0 adds the following backwards compatible changes and
  enhancements:
}
PARAGRAPH {
  <ol>

  <li value="7"><p>The new [sqlite3_config()] interface allows an application
  to customize the behavior of SQLite at run-time.  Customizations possible
  using [sqlite3_config()] include the following:</p>
  <ol type="a">
  <li><p>Specify an alternative mutex implementation using the
  [SQLITE_CONFIG_MUTEX] verb with the [sqlite3_mutex_methods] object.</p></li>
  <li><p>Specify an alternative malloc implementation using the
  [SQLITE_CONFIG_MALLOC] verb with the [sqlite3_mem_methods] object.</p></li>
  <li><p>Partially or fully disable the use of mutexes using
  [SQLITE_CONFIG_SINGLETHREAD], [SQLITE_CONFIG_MULTITHREAD] and
  [SQLITE_CONFIG_SERIALIZED].</p></li>
  </ol>
  </li>

  <li><p>A new flag [SQLITE_OPEN_NOMUTEX] is made available to the
  [sqlite3_open_v2()] interface.</p></li>

  <li><p>The new [sqlite3_status()] interface allows an application to query
  the performance status of SQLite at runtime.
  </p></li>

  <li><p>The [sqlite3_memory_used()] and [sqlite3_memory_highwater()]
  interfaces are deprecated.  The equivalent functionality is now available
  through [sqlite3_status()].</p></li>

  <li><p>The [sqlite3_initialize()] interface can be called to explicitly
  initialize the SQLite subsystem.  The [sqlite3_initialize()] interface is
  called automatically when invoking certain interfaces so the use of
  [sqlite3_initialize()] is not required, but it is recommended.</p></li>

  <li><p>The [sqlite3_shutdown()] interface causes SQLite to release any
  system resources (memory allocations, mutexes, open file handles)
  that might have been allocated by [sqlite3_initialize()].</p></li>

  <li><p>The [sqlite3_next_stmt()] interface allows an application to discover
  all [prepared statements] associated with a [database connection].</p></li>

  <li><p>Added the [page_count] PRAGMA for returning the size of the underlying
  database file in pages.</p></li>

  <li><p>Added a new [rtree | R*Tree index extension].</p></li>

  </ol>
}
</tcl>
