Documentation Source Text

  be able to read and write database files created by newer versions
  of SQLite, the default file format is set to 1 for maximum
  compatibility.

  The file format for a new database can be set at runtime using
  the [PRAGMA legacy_file_format] command.
}

COMPILE_OPTION {SQLITE_DEFAULT_JOURNAL_SIZE_LIMIT=<i>&lt;bytes&gt;</i>} {
  This option sets the size limit on rollback journal files in
  [journal_mode pragma | persistent journal mode].  When this 
  compile-time option is omitted there is no upper bound on the
  size of the rollback journal file.  The journal file size limit
  can be changed at run-time using the [journal_size_limit pragma].
}

COMPILE_OPTION {SQLITE_DEFAULT_MEMSTATUS=<i>&lt;1 or 0&gt;</i>} {
  This macro is used to determine whether or not the features enabled and
  disabled using the SQLITE_CONFIG_MEMSTATUS argument to [sqlite3_config()]
  are available by default. The default value is 1 ([SQLITE_CONFIG_MEMSTATUS]
  related features enabled).
}

Section {PRAGMA command syntax} syntax {PRAGMA}

BubbleDiagram pragma-stmt
BubbleDiagram pragma-value
</tcl>

<p>
A pragma can take either zero or one argument.  The argument is may be either
in parentheses or it may be separated from the pragma name by an equal sign.
The two syntaxes yield identical results.
In many pragmas, the argument is a boolean.  The boolean can be one of:
</p>

<center>
<b>1 yes true on<br>0 no false off</b>
</center>

<p>Keyword arguments can optionally appear in quotes.  
(Example:  <tt>'yes' &91;FALSE&93;</tt>.) Some pragmas
takes a string literal as their argument.  When pragma takes a keyword
argument, it will usually also take a numeric equivalent as well.
For example, "0" and "no" mean the same thing, as does "1" and "yes".
When querying the value of a setting, many pragmas return the number
rather than the keyword.</p>

<p>A pragma may have an optional database name before the pragma name.
The database name is the name of an [ATTACH]-ed database.  Or it can be
"main" or "temp" for the main and the TEMP databases.  If the optional
database name is omitted, "main" is assumed.  In some pragmas, the database
name is meaningless and is simply ignored.</p>

    <p>Databases created by the [ATTACH] command always use the same encoding
    as the main database.</p>
</li>

<tcl>Subsection full_column_names</tcl>
<li><p><b>PRAGMA full_column_names;
       <br>PRAGMA full_column_names = </b><i>boolean</i><b>;</b></p>
    <p>Query or change the full_column_names flag. This flag together 
    with the [short_column_names] flag determine
    the way SQLite assigns names to results returned by [SELECT] statements.

    Result columns are named by applying the following rules in order:

    <ol>
    <li><p>If there is an AS clause on the result, then the name of
        the column is the right-hand side of the AS clause.</p></li>
    <li><p>If the result is a general expression, not a just the name of
        a source table column,
        then the name of the result is a copy of the expression text.</p></li>
    <li><p>If the [short_column_names] pragma is ON, then the name of the
        result is the name of the source table column without the 
        source table name prefix:  COLUMN.</p></li>
    <li><p>If both pragmas [short_column_names] and [full_column_names]
        are OFF then

        case (2) applies for simple queries and case (5) applies for joins.
        </p></li>



    <li><p>The name of the result column is a combination of the source table
        and source column name:  TABLE.COLUMN</p></li>
    </ol>
</li>

<tcl>Subsection fullfsync</tcl>
<li><p><b>PRAGMA fullfsync
       <br>PRAGMA fullfsync = </b><i>boolean</i><b>;</b></p>
    <p>Query or change the fullfsync flag. This flag affects
    determines whether or not the F_FULLFSYNC syncing method is used
    on systems that support it.  The default value is off.  As of this
    writing (2006-02-10) only Mac OS X supports F_FULLFSYNC.
    </p>
</li>

<tcl>Subsection incremental_vacuum</tcl>
<li><p><b>PRAGMA incremental_vacuum</b><i>(N)</i><b>;</b></p>
    <p>The incremental_vacuum pragma causes up to <i>N</i> pages to
    be removed from the freelist.  The database file is truncated by
    the same amount.  The incremental_vacuum pragma has no effect if
    the database is not in
    <a href="#pragma_auto_vacuum">auto_vacuum==incremental</a> mode
    or if there are no pages on the freelist.  If there are fewer than
    <i>N</i> pages on the freelist, or if <i>N</i> is less than 1, or
    if <i>N</i> is omitted entirely, then the entire freelist is cleared.</p>

    <p>As of [version 3.4.0] (the first version that supports
    incremental_vacuum) this feature is still experimental.  Possible
    future changes include enhancing incremental vacuum to do
    defragmentation and node repacking just as the full-blown
    [VACUUM] command does.  And
    incremental vacuum may be promoted from a pragma to a separate
    SQL command, or perhaps some variation on the [VACUUM] command.
    Programmers are cautioned to not become enamored with the
    current syntax or functionality as it is likely to change.</p>
</li>

<tcl>Subsection journal_mode</tcl>
<li><p><b>PRAGMA journal_mode;
       <br>PRAGMA </b><i>database</i><b>.journal_mode;
       <br>PRAGMA journal_mode
              = <i>DELETE | TRUNCATE | PERSIST | MEMORY | OFF</i>
       <br>PRAGMA </b><i>database</i><b>.journal_mode
              = <i>DELETE | TRUNCATE | PERSIST | MEMORY | OFF</i></b></p>

    <p>This pragma queries or sets the journal mode for databases
    associated with the current [database connection].</p>

    <p>The first two forms of this pragma query the current journaling
    mode.  In the first form, the default journal_mode is returned.

    <p>The OFF journaling mode disables the rollback journal completely.
    No rollback journal is ever created and hence there is never a rollback
    journal to delete.  The OFF journaling mode disables the atomic
    commit and rollback capabilities of SQLite. The [ROLLBACK] command
    no longer works. If the application crashes
    in the middle of a transaction when the OFF journaling mode is
    set, then the database file will very likely go corrupt.</p>

    <p>Note that the journal_mode for an [in-memory database]
    is either MEMORY or OFF and can not be changed to a different value.
    An attempt to change the journal_mode of an [in-memory database] to
    any setting other than MEMORY or OFF is silently ignored.</p>
</li>

<tcl>Subsection journal_size_limit</tcl>
<li><p><b>
    PRAGMA journal_size_limit<br>
    PRAGMA journal_size_limit = </b><i>N</i> <b>;</b>

  <p>The second form of the pragma listed above is used to set a new limit
  in bytes for the specified database. A negative number implies no limit.
  Both the first and second forms of the pragma listed above return a single
  result row containing a single integer column - the value of the journal
  size limit in bytes. The default limit value is -1 (no limit), which
  may be overridden by defining the preprocessor macro
  [SQLITE_DEFAULT_JOURNAL_SIZE_LIMIT] at compile time.</p>

  <p>This pragma only operates on the single database specified prior
  to the pragma name (or on the "main" database if no database is specified.)
  There is no way to operate on all attached databases using a single
  PRAGMA statement, nor is there a way to set the limit to use for databases
  that will be attached in the future.
</li>


<tcl>Subsection legacy_file_format</tcl>
<li><p><b>PRAGMA legacy_file_format;
       <br>PRAGMA legacy_file_format = <i>boolean</i></b></p>
    <p>This pragma sets or queries the value of the legacy_file_format
    flag.  When this flag is on, new SQLite databases are created in
    a file format that is readable and writable by all versions of
    SQLite going back to 3.0.0.  When the flag is off, new databases
    are created using the latest file format which might not be
    readable or writable by versions of SQLite prior to 3.3.0.</p>

    <p>When the pragma is issued with no argument, it returns the
    setting of the flag.  This pragma does <u>not</u> tell which
    file format the current database is using.  It tells what format
    will be used by any newly created databases.</p>

    <p>This flag only affects newly created databases.  It has no

    <p>Then the locking mode applies only to the named database.  If no
    database name qualifier precedes the "locking_mode" keyword then
    the locking mode is applied to all databases, including any new
    databases added by subsequent [ATTACH] commands.</p>

   <p>The "temp" database (in which TEMP tables and indices are stored)
   and [in-memory databases]
   always uses exclusive locking mode.  The locking mode of temp and
   [in-memory databases] cannot
   be changed.  All other databases use the normal locking mode by default
   and are affected by this pragma.</p>
</li>

<tcl>Subsection page_size</tcl>
<li><p><b>PRAGMA page_size;
       <br>PRAGMA page_size = </b><i>bytes</i><b>;</b></p>

    Cache sharing is disabled by default.
    </p>

    <p>See [SQLite Shared-Cache Mode] for additional information.</p>
</li>

<tcl>Subsection reverse_unordered_selects</tcl>
<li><p><b>PRAGMA reverse_unordered_selects;
       <br>PRAGMA reverse_unordered_selects = </b><i>boolean</i><b>;</b></p>
    <p>When enabled, this PRAGMA causes [SELECT] statements without a
    an ORDER BY clause to emit their results in the reverse order of what
    they normally would.  This can help debug applications that are
    making invalid assumptions about the result order.<p>SQLite makes no
    guarantees about the order of results if a SELECT omits the ORDER BY
    clause.  Even so, the order of results does not change from one
    run to the next, and so many applications mistakenly come to depend

    </p>
</li>

<tcl>Subsection short_column_names</tcl>
<li><p><b>PRAGMA short_column_names;
       <br>PRAGMA short_column_names = </b><i>boolean</i><b>;</b></p>
    <p>Query or change the short-column-names flag. This flag affects
    the way SQLite names columns of data returned by [SELECT] statements.

    See the [full_column_names] pragma for full details.









    </p>
</li>

<tcl>Subsection synchronous</tcl>
<li><p><b>PRAGMA synchronous;
       <br>PRAGMA synchronous = </b>
          <i>0 | OFF | 1 | NORMAL | 2 | FULL</i><b>;</b></p>

    <br>

<tcl>Subsection temp_store_directory</tcl>
<li><p><b>PRAGMA temp_store_directory;
       <br>PRAGMA temp_store_directory = '</b><i>directory-name</i><b>';</b></p>
    <p>Query or change the setting of the "temp_store_directory" - the
    directory where files used for storing [temporary tables] and indices
    are kept.</p>


    <p>When the temp_store_directory setting is changed, all existing temporary
    tables, indices, triggers, and viewers are immediately deleted.  In
    practice, temp_store_directory should be set immediately after the 
    database is opened.</p>

    <p>Changing the temp_store_directory setting is <u>not</u> threadsafe.
    Never change the temp_store_directory setting if another thread
    within the application is running any SQLite interface at the same time.
    Doing so results in undefined behavior.  Changing the temp_store_directory
    setting writes to the [sqlite3_temp_directory] global
    variable and that global variable is not protected by a mutex.</p>

    <p>The value <i>directory-name</i> should be enclosed in single quotes.
    To revert the directory to the default, set the <i>directory-name</i> to
    an empty string, e.g., <i>PRAGMA temp_store_directory = ''</i>.  An
    error is raised if <i>directory-name</i> is not found or is not
    writable. </p>

    <p>The default directory for temporary files depends on the OS.  Some
    OS interfaces may choose to ignore this variable in place temporary
    files in some other directory different from the directory specified








    here.  In that sense, this pragma is only advisory.</p>
    </li>
</ul>

<tcl>Section {Pragmas to query the database schema} schema</tcl>

<ul>
<tcl>Subsection database_list</tcl>