reference/pdo_sqlite/PDO/sqliteCreateAggregate.xml
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<type>mixed</type><methodname><replaceable>step</replaceable></methodname>
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<methodparam><type>mixed</type><parameter>context</parameter></methodparam>
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<methodparam><type>int</type><parameter>rownumber</parameter></methodparam>
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<methodparam><type>mixed</type><parameter>value1</parameter></methodparam>
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<methodparam choice="opt"><type>mixed</type><parameter>value2</parameter></methodparam>
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<methodparam choice="opt"><type>mixed</type><parameter>..</parameter></methodparam>
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<methodparam><type>mixed</type><parameter>value</parameter></methodparam>
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<methodparam rep="repeat"><type>mixed</type><parameter>values</parameter></methodparam>
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</methodsynopsis>
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</para>
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<para>
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<varname>context</varname> will be &null; for the first row; on
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subsequent rows it will have the value that was previously returned
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from the step function; you should use this to maintain the aggregate
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state.
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</para>
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<para>
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<varname>rownumber</varname> will hold the current row number.
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</para>
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<para>
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<variablelist>
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<varlistentry>
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<term><parameter>context</parameter></term>
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<listitem>
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<para>
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&null; for the first row; on subsequent rows it will have the value
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that was previously returned from the step function; you should use
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this to maintain the aggregate state.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>rownumber</parameter></term>
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<listitem>
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<para>
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The current row number.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>value</parameter></term>
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<listitem>
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<para>
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The first argument passed to the aggregate.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>values</parameter></term>
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<listitem>
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<para>
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Further arguments passed to the aggregate.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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The return value of this function will be used as the
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<parameter>context</parameter> argument in the next call of the step or
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finalize functions.
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Callback function to aggregate the "stepped" data from each row.
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Once all the rows have been processed, this function will be called
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and it should then take the data from the aggregation context and
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return the result. Callback functions should return a type understood
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return the result. This callback function should return a type understood
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by SQLite (i.e. <link
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linkend="language.types.intro">scalar type</link>).
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</para>
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<methodsynopsis>
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<type>mixed</type><methodname><replaceable>fini</replaceable></methodname>
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<methodparam><type>mixed</type><parameter>context</parameter></methodparam>
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<methodparam><type>int</type><parameter>rownumber</parameter></methodparam>
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<methodparam><type>int</type><parameter>rowcount</parameter></methodparam>
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</methodsynopsis>
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</para>
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<para>
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<varname>context</varname> will hold the return value from the very
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last call to the step function.
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</para>
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<para>
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<varname>rownumber</varname> will hold the number of rows over which
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the aggregate was performed.
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</para>
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<para>
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<variablelist>
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<varlistentry>
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<term><parameter>context</parameter></term>
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<listitem>
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<para>
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Holds the return value from the very last call to the step function.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>rowcount</parameter></term>
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<listitem>
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<para>
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Holds the number of rows over which the aggregate was performed.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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The return value of this function will be used as the return value for
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the aggregate.
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</para>
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}
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$insert = null;
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function max_len_step(&$context, $rownumber, $string)
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function max_len_step($context, $rownumber, $string)
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{
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if (strlen($string) > $context) {
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$context = strlen($string);
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return $context;
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}
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function max_len_finalize(&$context, $rownumber)
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function max_len_finalize($context, $rowcount)
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{
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return $context;
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return $context === null ? 0 : $context;
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}
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$db->sqliteCreateAggregate('max_len', 'max_len_step', 'max_len_finalize');
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In this example, we are creating an aggregating function that will
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calculate the length of the longest string in one of the columns of the
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table. For each row, the <literal>max_len_step</literal> function is
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called and passed a <parameter>context</parameter> parameter. The context
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called and passed a <literal>$context</literal> parameter. The context
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parameter is just like any other PHP variable and be set to hold an array
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or even an object value. In this example, we are simply using it to hold
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the maximum length we have seen so far; if the
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<parameter>string</parameter> has a length longer than the current
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<literal>$string</literal> has a length longer than the current
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maximum, we update the context to hold this new maximum length.
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</para>
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<para>
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After all of the rows have been processed, SQLite calls the
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<literal>max_len_finalize</literal> function to determine the aggregate
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result. Here, we could perform some kind of calculation based on the
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data found in the <parameter>context</parameter>. In our simple example
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data found in the <literal>$context</literal>. In our simple example
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though, we have been calculating the result as the query progressed, so we
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simply need to return the context value.
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</para>
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native SQL functions.
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</para>
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</tip>
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<note>
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<para>
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This method is not available with the SQLite2 driver.
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Use the old style sqlite API for that instead.
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</para>
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</note>
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</refsect1>
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