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      <a name="window-functions">
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      14.20 Window Functions
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      <a href="window-function-descriptions.html">
       14.20.1 Window Function Descriptions
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      <a href="window-functions-usage.html">
       14.20.2 Window Function Concepts and Syntax
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       14.20.3 Window Function Frame Specification
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       14.20.4 Named Windows
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      <a href="window-function-restrictions.html">
       14.20.5 Window Function Restrictions
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  <p>
   MySQL supports window functions that, for each row from a query,
      perform a calculation using rows related to that row. The
      following sections discuss how to use window functions, including
      descriptions of the
   <code class="literal">
    OVER
   </code>
   and
   <code class="literal">
    WINDOW
   </code>
   clauses. The first section provides
      descriptions of the nonaggregate window functions. For
      descriptions of the aggregate window functions, see
   <a class="xref" href="aggregate-functions.html" title="14.19.1 Aggregate Function Descriptions">
    Section 14.19.1, “Aggregate Function Descriptions”
   </a>
   .
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  <p>
   For information about optimization and window functions, see
   <a class="xref" href="window-function-optimization.html" title="10.2.1.21 Window Function Optimization">
    Section 10.2.1.21, “Window Function Optimization”
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   .
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