zone="syntax-window-functions">
    <primary>window function</primary>
    <secondary>invocation</secondary>
   </indexterm>

   <indexterm zone="syntax-window-functions">
    <primary>OVER clause</primary>
   </indexterm>

   <para>
    A <firstterm>window function call</firstterm> represents the application
    of an aggregate-like function over some portion of the rows selected
    by a query.  Unlike non-window aggregate calls, this is not tied
    to grouping of the selected rows into a single output row &mdash; each
    row remains separate in the query output.  However the window function
    has access to all the rows that would be part of the current row's
    group according to the grouping specification (<literal>PARTITION BY</literal>
    list) of the window function call.
    The syntax of a window function call is one of the following:

<synopsis>
<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER <replaceable>window_name</replaceable>
<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER ( <replaceable class="parameter">window_definition</replaceable> )
<replaceable>function_name</replaceable> ( * ) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER <replaceable>window_name</replaceable>
<replaceable>function_name</replaceable> ( * ) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER ( <replaceable class="parameter">window_definition</replaceable> )
</synopsis>
    where <replaceable class="parameter">window_definition</replaceable>
    has the syntax
<synopsis>
[ <replaceable class="parameter">existing_window_name</replaceable> ]
[ PARTITION BY <replaceable class="parameter">expression</replaceable> [, ...] ]
[ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC | USING <replaceable class="parameter">operator</replaceable> ] [ NULLS { FIRST | LAST } ] [, ...] ]
[ <replaceable class="parameter">frame_clause</replaceable> ]
</synopsis>
    The optional <replaceable class="parameter">frame_clause</replaceable>
    can be one of
<synopsis>
{ RANGE | ROWS | GROUPS } <replaceable>frame_start</replaceable> [ <replaceable>frame_exclusion</replaceable> ]
{ RANGE | ROWS | GROUPS } BETWEEN <replaceable>frame_start</replaceable> AND <replaceable>frame_end</replaceable> [ <replaceable>frame_exclusion</replaceable> ]
</synopsis>
    where <replaceable>frame_start</replaceable>
    and <replaceable>frame_end</replaceable> can be one of
<synopsis>
UNBOUNDED PRECEDING
<replaceable>offset</replaceable> PRECEDING
CURRENT ROW
<replaceable>offset</replaceable> FOLLOWING
UNBOUNDED FOLLOWING
</synopsis>
    and <replaceable>frame_exclusion</replaceable> can be one of
<synopsis>
EXCLUDE CURRENT ROW
EXCLUDE GROUP
EXCLUDE TIES
EXCLUDE NO OTHERS
</synopsis>
   </para>

   <para>
    Here, <replaceable>expression</replaceable> represents any value
    expression that does not itself contain window function calls.
   </para>

   <para>
    <replaceable>window_name</replaceable> is a reference to a named window
    specification defined in the query's <literal>WINDOW</literal> clause.
    Alternatively, a full <replaceable>window_definition</replaceable> can
    be given within parentheses, using the same syntax as for defining a
    named window in the <literal>WINDOW</literal> clause; see the
    <xref linkend="sql-select"/> reference page for details.  It's worth
    pointing out that <literal>OVER wname</literal> is not exactly equivalent to
    <literal>OVER (wname ...)</literal>; the latter implies copying and modifying the
    window definition, and will be rejected if the referenced window
    specification includes a