159 lines
5.7 KiB
HTML
159 lines
5.7 KiB
HTML
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<!-- keywords: sqlite3_stmt_explain -->
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<div class=nosearch>
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<a href="../c3ref/intro.html"><h2>SQLite C Interface</h2></a>
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<h2>Change The EXPLAIN Setting For A Prepared Statement</h2>
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</div>
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<blockquote><pre>
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int sqlite3_stmt_explain(sqlite3_stmt *pStmt, int eMode);
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</pre></blockquote>
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<p>
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The sqlite3_stmt_explain(S,E) interface changes the EXPLAIN
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setting for <a href="../c3ref/stmt.html">prepared statement</a> S. If E is zero, then S becomes
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a normal prepared statement. If E is 1, then S behaves as if
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its SQL text began with "<a href="../lang_explain.html">EXPLAIN</a>". If E is 2, then S behaves as if
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its SQL text began with "<a href="../eqp.html">EXPLAIN QUERY PLAN</a>".</p>
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<p>Calling sqlite3_stmt_explain(S,E) might cause S to be reprepared.
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SQLite tries to avoid a reprepare, but a reprepare might be necessary
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on the first transition into EXPLAIN or EXPLAIN QUERY PLAN mode.</p>
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<p>Because of the potential need to reprepare, a call to
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sqlite3_stmt_explain(S,E) will fail with SQLITE_ERROR if S cannot be
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reprepared because it was created using <a href="../c3ref/prepare.html">sqlite3_prepare()</a> instead of
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the newer <a href="../c3ref/prepare.html">sqlite3_prepare_v2()</a> or <a href="../c3ref/prepare.html">sqlite3_prepare_v3()</a> interfaces and
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hence has no saved SQL text with which to reprepare.</p>
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<p>Changing the explain setting for a prepared statement does not change
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the original SQL text for the statement. Hence, if the SQL text originally
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began with EXPLAIN or EXPLAIN QUERY PLAN, but sqlite3_stmt_explain(S,0)
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is called to convert the statement into an ordinary statement, the EXPLAIN
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or EXPLAIN QUERY PLAN keywords will still appear in the sqlite3_sql(S)
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output, even though the statement now acts like a normal SQL statement.</p>
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<p>This routine returns SQLITE_OK if the explain mode is successfully
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changed, or an error code if the explain mode could not be changed.
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The explain mode cannot be changed while a statement is active.
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Hence, it is good practice to call <a href="../c3ref/reset.html">sqlite3_reset(S)</a>
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immediately prior to calling sqlite3_stmt_explain(S,E).
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</p><p>See also lists of
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<a href="../c3ref/objlist.html">Objects</a>,
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<a href="../c3ref/constlist.html">Constants</a>, and
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<a href="../c3ref/funclist.html">Functions</a>.</p>
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