pragma.html

来自「sqlite 3.3.8 支持加密的版本」· HTML 代码 · 共 657 行 · 第 1/3 页

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          </blockquote>
          <br />
          <a name="pragma_temp_store_directory"></a></li>
        <li>
          <p>
            <b>PRAGMA temp_store_directory;
              <br />
              PRAGMA temp_store_directory = 'directory-name';</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. This setting lasts
            for the duration of the current connection only and resets to its default value
            for each new connection opened.
          </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>
            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. For Unix/Linux/OSX,
            the default is the is the first writable directory found in the list of: <b>/var/tmp,
              /usr/tmp, /tmp,</b> and <b><i>current-directory</i></b>. For Windows NT, the default
            directory is determined by Windows, generally <b>C:\Documents and Settings\<i>user-name</i>\Local
              Settings\Temp\</b>. Temporary files created by SQLite are unlinked immediately
            after opening, so that the operating system can automatically delete the files when
            the SQLite process exits. Thus, temporary files are not normally visible through
            <i>ls</i> or <i>dir</i> commands.</p>
        </li>
      </ul>
      <hr />
      <a name="schema"></a>
      <h1>
        Pragmas to query the database schema</h1>
      <ul>
        <a name="pragma_database_list"></a>
        <li>
          <p>
            <b>PRAGMA database_list;</b></p>
          <p>
            For each open database, invoke the callback function once with information about
            that database. Arguments include the index and the name the database was attached
            with. The first row will be for the main database. The second row will be for the
            database used to store temporary tables.</p>
          <a name="pragma_foreign_key_list"></a></li>
        <li>
          <p>
            <b>PRAGMA foreign_key_list(</b><i>table-name</i><b>);</b></p>
          <p>
            For each foreign key that references a column in the argument table, invoke the
            callback function with information about that foreign key. The callback function
            will be invoked once for each column in each foreign key.</p>
          <a name="pragma_index_info"></a></li>
        <li>
          <p>
            <b>PRAGMA index_info(</b><i>index-name</i><b>);</b></p>
          <p>
            For each column that the named index references, invoke the callback function once
            with information about that column, including the column name, and the column number.</p>
          <a name="pragma_index_list"></a></li>
        <li>
          <p>
            <b>PRAGMA index_list(</b><i>table-name</i><b>);</b></p>
          <p>
            For each index on the named table, invoke the callback function once with information
            about that index. Arguments include the index name and a flag to indicate whether
            or not the index must be unique.</p>
          <a name="pragma_table_info"></a></li>
        <li>
          <p>
            <b>PRAGMA table_info(</b><i>table-name</i><b>);</b></p>
          <p>
            For each column in the named table, invoke the callback function once with information
            about that column, including the column name, data type, whether or not the column
            can be NULL, and the default value for the column.</p>
        </li>
      </ul>
      <hr />
      <a name="version"></a>
      <h1>
        Pragmas to query/modify version values</h1>
      <ul>
        <a name="pragma_schema_version"></a><a name="pragma_user_version"></a>
        <li>
          <p>
            <b>PRAGMA [database.]schema_version;
              <br />
              PRAGMA [database.]schema_version = </b><i>integer </i><b>;
                <br />
                PRAGMA [database.]user_version;
                <br />
                PRAGMA [database.]user_version = </b><i>integer </i><b>;</b>
          </p>
          <p>
            The pragmas schema_version and user_version are used to set or get the value of
            the schema-version and user-version, respectively. Both the schema-version and the
            user-version are 32-bit signed integers stored in the database header.</p>
          <p>
            The schema-version is usually only manipulated internally by SQLite. It is incremented
            by SQLite whenever the database schema is modified (by creating or dropping a table
            or index). The schema version is used by SQLite each time a query is executed to
            ensure that the internal cache of the schema used when compiling the SQL query matches
            the schema of the database against which the compiled query is actually executed.
            Subverting this mechanism by using "PRAGMA schema_version" to modify the schema-version
            is potentially dangerous and may lead to program crashes or database corruption.
            Use with caution!</p>
          <p>
            The user-version is not used internally by SQLite. It may be used by applications
            for any purpose.</p>
        </li>
      </ul>
      <hr />
      <a name="debug"></a>
      <h1>
        Pragmas to debug the library</h1>
      <ul>
        <a name="pragma_integrity_check"></a>
        <li>
          <p>
            <b>PRAGMA integrity_check;</b></p>
          <p>
            The command does an integrity check of the entire database. It looks for out-of-order
            records, missing pages, malformed records, and corrupt indices. If any problems
            are found, then a single string is returned which is a description of all problems.
            If everything is in order, "ok" is returned.</p>
          <a name="pragma_parser_trace"></a></li>
        <li>
          <p>
            <b>PRAGMA parser_trace = ON; </b>(1)<b>
              <br />
              PRAGMA parser_trace = OFF;</b> (0)</p>
          <p>
            Turn tracing of the SQL parser inside of the SQLite library on and off. This is
            used for debugging. This only works if the library is compiled without the NDEBUG
            macro.
          </p>
          <a name="pragma_vdbe_trace"></a></li>
        <li>
          <p>
            <b>PRAGMA vdbe_trace = ON; </b>(1)<b>
              <br />
              PRAGMA vdbe_trace = OFF;</b> (0)</p>
          <p>
            Turn tracing of the virtual database engine inside of the SQLite library on and
            off. This is used for debugging. See the <a href="vdbe.html#trace">VDBE documentation</a>
            for more information.</p>
          <a name="pragma_vdbe_listing"></a></li>
        <li>
          <p>
            <b>PRAGMA vdbe_listing = ON; </b>(1)<b>
              <br />
              PRAGMA vdbe_listing = OFF;</b> (0)</p>
          <p>
            Turn listings of virtual machine programs on and off. With listing is on, the entire
            content of a program is printed just prior to beginning execution. This is like
            automatically executing an EXPLAIN prior to each statement. The statement executes
            normally after the listing is printed. This is used for debugging. See the <a href="vdbe.html#trace">
              VDBE documentation</a> for more information.</p>
        </li>
      </ul>
      <p>
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