function.pdo-sqlitecreateaggregate.html

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      <p class="para">
       <var class="varname">context</var> will hold the return value from the very
       last call to the step function.
      </p>
      <p class="para">
       <var class="varname">rownumber</var> will hold the number of rows over which
       the aggregate was performed.
      </p>
      <p class="para">
       The return value of this function will be used as the return value for
       the aggregate.
      </p>
     </dd>

    </dt>

    <dt>

     <span class="term"><i><tt class="parameter">num_args</tt></i>
</span>

     <dd>

      <p class="para">
       Hint to the SQLite parser if the callback function accepts a
       predetermined number of arguments.
      </p>
     </dd>

    </dt>

   </dl>

  </p>
 </div>


 <div class="refsect1 returnvalues">
  <h3 class="title">Return Values</h3>
  <p class="para">
   Returns <b><tt>TRUE</tt></b> on success or <b><tt>FALSE</tt></b> on failure.
  </p>
 </div>


 <div class="refsect1 examples">
  <h3 class="title">Examples</h3>
  <p class="para">
   <div class="example">
    <p><b>Example #1 max_length aggregation function example</b></p>
    <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br />$data&nbsp;</span><span style="color: #007700">=&nbsp;array(<br />&nbsp;&nbsp;&nbsp;</span><span style="color: #DD0000">'one'</span><span style="color: #007700">,<br />&nbsp;&nbsp;&nbsp;</span><span style="color: #DD0000">'two'</span><span style="color: #007700">,<br />&nbsp;&nbsp;&nbsp;</span><span style="color: #DD0000">'three'</span><span style="color: #007700">,<br />&nbsp;&nbsp;&nbsp;</span><span style="color: #DD0000">'four'</span><span style="color: #007700">,<br />&nbsp;&nbsp;&nbsp;</span><span style="color: #DD0000">'five'</span><span style="color: #007700">,<br />&nbsp;&nbsp;&nbsp;</span><span style="color: #DD0000">'six'</span><span style="color: #007700">,<br />&nbsp;&nbsp;&nbsp;</span><span style="color: #DD0000">'seven'</span><span style="color: #007700">,<br />&nbsp;&nbsp;&nbsp;</span><span style="color: #DD0000">'eight'</span><span style="color: #007700">,<br />&nbsp;&nbsp;&nbsp;</span><span style="color: #DD0000">'nine'</span><span style="color: #007700">,<br />&nbsp;&nbsp;&nbsp;</span><span style="color: #DD0000">'ten'</span><span style="color: #007700">,<br />&nbsp;&nbsp;&nbsp;);<br /></span><span style="color: #0000BB">$db&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">PDO</span><span style="color: #007700">(</span><span style="color: #DD0000">'sqlite::memory:'</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$db</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">exec</span><span style="color: #007700">(</span><span style="color: #DD0000">"CREATE&nbsp;TABLE&nbsp;strings(a)"</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$insert&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">$db</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">prepare</span><span style="color: #007700">(</span><span style="color: #DD0000">'INSERT&nbsp;INTO&nbsp;strings&nbsp;VALUES&nbsp;(?)'</span><span style="color: #007700">);<br />foreach&nbsp;(</span><span style="color: #0000BB">$data&nbsp;</span><span style="color: #007700">as&nbsp;</span><span style="color: #0000BB">$str</span><span style="color: #007700">)&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #0000BB">$insert</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">execute</span><span style="color: #007700">(array(</span><span style="color: #0000BB">$str</span><span style="color: #007700">));<br />}<br /></span><span style="color: #0000BB">$insert&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">null</span><span style="color: #007700">;<br /><br />function&nbsp;</span><span style="color: #0000BB">max_len_step</span><span style="color: #007700">(&amp;</span><span style="color: #0000BB">$context</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$rownumber</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$string</span><span style="color: #007700">)&nbsp;<br />{<br />&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(</span><span style="color: #0000BB">strlen</span><span style="color: #007700">(</span><span style="color: #0000BB">$string</span><span style="color: #007700">)&nbsp;&gt;&nbsp;</span><span style="color: #0000BB">$context</span><span style="color: #007700">)&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #0000BB">$context&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">strlen</span><span style="color: #007700">(</span><span style="color: #0000BB">$string</span><span style="color: #007700">);<br />&nbsp;&nbsp;&nbsp;&nbsp;}<br />}<br /><br />function&nbsp;</span><span style="color: #0000BB">max_len_finalize</span><span style="color: #007700">(&amp;</span><span style="color: #0000BB">$context</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$rownumber</span><span style="color: #007700">)&nbsp;<br />{<br />&nbsp;&nbsp;&nbsp;&nbsp;return&nbsp;</span><span style="color: #0000BB">$context</span><span style="color: #007700">;<br />}<br /><br /></span><span style="color: #0000BB">$db</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">sqliteCreateAggregate</span><span style="color: #007700">(</span><span style="color: #DD0000">'max_len'</span><span style="color: #007700">,&nbsp;</span><span style="color: #DD0000">'max_len_step'</span><span style="color: #007700">,&nbsp;</span><span style="color: #DD0000">'max_len_finalize'</span><span style="color: #007700">);<br /><br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">$db</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">query</span><span style="color: #007700">(</span><span style="color: #DD0000">'SELECT&nbsp;max_len(a)&nbsp;from&nbsp;strings'</span><span style="color: #007700">)-&gt;</span><span style="color: #0000BB">fetchAll</span><span style="color: #007700">());<br /><br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
    </div>

   </div>
  </p>
  <p class="para">
   In this example, we are creating an aggregating function that will
   calculate the length of the longest string in one of the columns of the
   table.  For each row, the <i>max_len_step</i> function is
   called and passed a <i><tt class="parameter">context</tt></i>
 parameter.  The context
   parameter is just like any other PHP variable and be set to hold an array
   or even an object value.  In this example, we are simply using it to hold
   the maximum length we have seen so far; if the
   <i><tt class="parameter">string</tt></i>
 has a length longer than the current
   maximum, we update the context to hold this new maximum length.
  </p>
  <p class="para">
   After all of the rows have been processed, SQLite calls the
   <i>max_len_finalize</i> function to determine the aggregate
   result.  Here, we could perform some kind of calculation based on the
   data found in the <i><tt class="parameter">context</tt></i>
.  In our simple example
   though, we have been calculating the result as the query progressed, so we
   simply need to return the context value.
  </p>
  <div class="tip"><b class="tip">Tip</b>
   <p class="para">
    It is NOT recommended for you to store a copy of the values in the context
    and then process them at the end, as you would cause SQLite to use a lot of
    memory to process the query - just think of how much memory you would need
    if a million rows were stored in memory, each containing a string 32 bytes
    in length.
   </p>
  </div>
  <div class="tip"><b class="tip">Tip</b>
   <p class="para">
    You can use <a href="function.pdo-sqlitecreatefunction.html" class="xref">PDO->sqliteCreateFunction</a> and
    <a href="function.pdo-sqlitecreateaggregate.html" class="xref">PDO->sqliteCreateAggregate</a> to override SQLite
    native SQL functions.
   </p>
  </div>
  <blockquote><p><b class="note">Note</b>: 
   
    This method is not available with the SQLite2 driver.
    Use the old style sqlite API for that instead.
   <br />
  </p></blockquote>

 </div>



 <div class="refsect1 seealso">
  <h3 class="title">See Also</h3>
  <p class="para">
   <ul class="simplelist">
    <li class="member"><a href="function.pdo-sqlitecreatefunction.html" class="xref">PDO->sqliteCreateFunction</a></li>
    <li class="member"><a href="function.sqlite-create-function.html" class="function" rel="rdfs-seeAlso">sqlite_create_function()</a></li>
    <li class="member"><a href="function.sqlite-create-aggregate.html" class="function" rel="rdfs-seeAlso">sqlite_create_aggregate()</a></li>
   </ul>
  </p>
 </div>


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