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+<!-- keywords: sqlite3_vtab_nochange -->
+<div class=nosearch>
+<a href="../c3ref/intro.html"><h2>SQLite C Interface</h2></a>
+<h2>Determine If Virtual Table Column Access Is For UPDATE</h2>
+</div>
+<blockquote><pre>
+int sqlite3_vtab_nochange(sqlite3_context*);
+</pre></blockquote>
+<p>
+If the sqlite3_vtab_nochange(X) routine is called within the <a href="../vtab.html#xcolumn">xColumn</a>
+method of a <a href="../vtab.html">virtual table</a>, then it might return true if the
+column is being fetched as part of an UPDATE operation during which the
+column value will not change.  The virtual table implementation can use
+this hint as permission to substitute a return value that is less
+expensive to compute and that the corresponding
+<a href="../vtab.html#xupdate">xUpdate</a> method understands as a "no-change" value.</p>
+
+<p>If the <a href="../vtab.html#xcolumn">xColumn</a> method calls sqlite3_vtab_nochange() and finds that
+the column is not changed by the UPDATE statement, then the xColumn
+method can optionally return without setting a result, without calling
+any of the <a href="../c3ref/result_blob.html">sqlite3_result_xxxxx() interfaces</a>.
+In that case, <a href="../c3ref/value_blob.html">sqlite3_value_nochange(X)</a> will return true for the
+same column in the <a href="../vtab.html#xupdate">xUpdate</a> method.</p>
+
+<p>The sqlite3_vtab_nochange() routine is an optimization.  Virtual table
+implementations should continue to give a correct answer even if the
+sqlite3_vtab_nochange() interface were to always return false.  In the
+current implementation, the sqlite3_vtab_nochange() interface does always
+returns false for the enhanced <a href="../lang_update.html#upfrom">UPDATE FROM</a> statement.
+</p><p>See also lists of
+  <a href="../c3ref/objlist.html">Objects</a>,
+  <a href="../c3ref/constlist.html">Constants</a>, and
+  <a href="../c3ref/funclist.html">Functions</a>.</p>
+