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      <a name="aggregate-functions-and-modifiers">
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      14.19 Aggregate Functions
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    <dt>
     <span class="section">
      <a href="aggregate-functions.html">
       14.19.1 Aggregate Function Descriptions
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      <a href="group-by-modifiers.html">
       14.19.2 GROUP BY Modifiers
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      <a href="group-by-handling.html">
       14.19.3 MySQL Handling of GROUP BY
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      <a href="group-by-functional-dependence.html">
       14.19.4 Detection of Functional Dependence
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  <p>
   Aggregate functions operate on sets of values. They are often used
      with a
   <code class="literal">
    GROUP BY
   </code>
   clause to group values into
      subsets. This section describes most aggregate functions. For
      information about aggregate functions that operate on geometry
      values, see
   <a class="xref" href="spatial-aggregate-functions.html" title="14.16.12 Spatial Aggregate Functions">
    Section 14.16.12, “Spatial Aggregate Functions”
   </a>
   .
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