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<title>Determine The Collation For a Virtual Table Constraint</title>
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<!-- keywords: sqlite3_vtab_collation -->
<div class=nosearch>
<a href="intro.html"><h2>SQLite C Interface</h2></a>
<h2>Determine The Collation For a Virtual Table Constraint</h2>
</div>
<blockquote><pre>
const char *sqlite3_vtab_collation(sqlite3_index_info*,int);
</pre></blockquote>
<p>
This function may only be called from within a call to the <a href="../vtab.html#xbestindex">xBestIndex</a>
method of a <a href="../vtab.html">virtual table</a>. This function returns a pointer to a string
that is the name of the appropriate collation sequence to use for text
comparisons on the constraint identified by its arguments.</p>
<p>The first argument must be the pointer to the <a href="../c3ref/index_info.html">sqlite3_index_info</a> object
that is the first parameter to the xBestIndex() method. The second argument
must be an index into the aConstraint[] array belonging to the
sqlite3_index_info structure passed to xBestIndex.</p>
<p>Important:
The first parameter must be the same pointer that is passed into the
xBestMethod() method. The first parameter may not be a pointer to a
different <a href="../c3ref/index_info.html">sqlite3_index_info</a> object, even an exact copy.</p>
<p>The return value is computed as follows:</p>
<p><ol>
<li><p> If the constraint comes from a WHERE clause expression that contains
a <a href="../lang_expr.html#collateop">COLLATE operator</a>, then the name of the collation specified by
that COLLATE operator is returned.
<li><p> If there is no COLLATE operator, but the column that is the subject
of the constraint specifies an alternative collating sequence via
a <a href="../lang_createtable.html#collateclause">COLLATE clause</a> on the column definition within the CREATE TABLE
statement that was passed into <a href="../c3ref/declare_vtab.html">sqlite3_declare_vtab()</a>, then the
name of that alternative collating sequence is returned.
<li><p> Otherwise, "BINARY" is returned.
</ol>
</p><p>See also lists of
<a href="objlist.html">Objects</a>,
<a href="constlist.html">Constants</a>, and
<a href="funclist.html">Functions</a>.</p>
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