167 lines
6.2 KiB
HTML
167 lines
6.2 KiB
HTML
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<!-- keywords: sqlite3_vtab_rhs_value -->
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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>Constraint values in xBestIndex()</h2>
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</div>
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<blockquote><pre>
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int sqlite3_vtab_rhs_value(sqlite3_index_info*, int, sqlite3_value **ppVal);
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</pre></blockquote>
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<p>
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This API may only be used from within the <a href="../vtab.html#xbestindex">xBestIndex method</a>
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of a <a href="../vtab.html">virtual table</a> implementation. The result of calling this interface
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from outside of an xBestIndex method are undefined and probably harmful.</p>
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<p>When the sqlite3_vtab_rhs_value(P,J,V) interface is invoked from within
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the <a href="../vtab.html#xbestindex">xBestIndex</a> method of a <a href="../vtab.html">virtual table</a> implementation, with P being
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a copy of the <a href="../c3ref/index_info.html">sqlite3_index_info</a> object pointer passed into xBestIndex and
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J being a 0-based index into P->aConstraint[], then this routine
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attempts to set *V to the value of the right-hand operand of
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that constraint if the right-hand operand is known. If the
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right-hand operand is not known, then *V is set to a NULL pointer.
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The sqlite3_vtab_rhs_value(P,J,V) interface returns SQLITE_OK if
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and only if *V is set to a value. The sqlite3_vtab_rhs_value(P,J,V)
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inteface returns SQLITE_NOTFOUND if the right-hand side of the J-th
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constraint is not available. The sqlite3_vtab_rhs_value() interface
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can return an result code other than SQLITE_OK or SQLITE_NOTFOUND if
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something goes wrong.</p>
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<p>The sqlite3_vtab_rhs_value() interface is usually only successful if
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the right-hand operand of a constraint is a literal value in the original
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SQL statement. If the right-hand operand is an expression or a reference
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to some other column or a <a href="../c3ref/bind_blob.html">host parameter</a>, then sqlite3_vtab_rhs_value()
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will probably return <a href="../rescode.html#notfound">SQLITE_NOTFOUND</a>.</p>
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<p>Some constraints, such as <a href="../c3ref/c_index_constraint_eq.html">SQLITE_INDEX_CONSTRAINT_ISNULL</a> and
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<a href="../c3ref/c_index_constraint_eq.html">SQLITE_INDEX_CONSTRAINT_ISNOTNULL</a>, have no right-hand operand. For such
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constraints, sqlite3_vtab_rhs_value() always returns SQLITE_NOTFOUND.</p>
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<p>The <a href="../c3ref/value.html">sqlite3_value</a> object returned in *V is a protected sqlite3_value
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and remains valid for the duration of the xBestIndex method call.
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When xBestIndex returns, the sqlite3_value object returned by
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sqlite3_vtab_rhs_value() is automatically deallocated.</p>
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<p>The "_rhs_" in the name of this routine is an abbreviation for
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"Right-Hand Side".
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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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