120 lines
4.4 KiB
HTML
120 lines
4.4 KiB
HTML
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<title>Determine If Virtual Table Column Access Is For UPDATE</title>
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<!-- keywords: sqlite3_vtab_nochange -->
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<a href="intro.html"><h2>SQLite C Interface</h2></a>
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<h2>Determine If Virtual Table Column Access Is For UPDATE</h2>
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</div>
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<blockquote><pre>
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int sqlite3_vtab_nochange(sqlite3_context*);
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</pre></blockquote>
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<p>
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If the sqlite3_vtab_nochange(X) routine is called within the <a href="../vtab.html#xcolumn">xColumn</a>
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method of a <a href="../vtab.html">virtual table</a>, then it returns true if and only if the
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column is being fetched as part of an UPDATE operation during which the
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column value will not change. Applications might use this to substitute
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a return value that is less expensive to compute and that the corresponding
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<a href="../vtab.html#xupdate">xUpdate</a> method understands as a "no-change" value.</p>
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<p>If the <a href="../vtab.html#xcolumn">xColumn</a> method calls sqlite3_vtab_nochange() and finds that
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the column is not changed by the UPDATE statement, then the xColumn
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method can optionally return without setting a result, without calling
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any of the <a href="../c3ref/result_blob.html">sqlite3_result_xxxxx() interfaces</a>.
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In that case, <a href="../c3ref/value_blob.html">sqlite3_value_nochange(X)</a> will return true for the
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same column in the <a href="../vtab.html#xupdate">xUpdate</a> method.
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</p><p>See also lists of
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<a href="objlist.html">Objects</a>,
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<a href="constlist.html">Constants</a>, and
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<a href="funclist.html">Functions</a>.</p>
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