doc/src/sgml/func/func-aggregate.sgml - master - githubmirror/postgres

doc/src/sgml/func/func-aggregate.sgml
1 420 строк53 KB
Masahiko Sawada
Add min() and max() aggregate support for uuid.
01 июл 2026, 21:42
01 июл 2026, 21:422e606d7
 <sect1 id="functions-aggregate">
  <title>Aggregate Functions</title>

  <indexterm zone="functions-aggregate">
   <primary>aggregate function</primary>
   <secondary>built-in</secondary>
  </indexterm>

  <para>
   <firstterm>Aggregate functions</firstterm> compute a single result
   from a set of input values.  The built-in general-purpose aggregate
   functions are listed in <xref linkend="functions-aggregate-table"/>
   while statistical aggregates are in <xref
   linkend="functions-aggregate-statistics-table"/>.
   The built-in within-group ordered-set aggregate functions
   are listed in <xref linkend="functions-orderedset-table"/>
   while the built-in within-group hypothetical-set ones are in <xref
   linkend="functions-hypothetical-table"/>.  Grouping operations,
   which are closely related to aggregate functions, are listed in
   <xref linkend="functions-grouping-table"/>.
   The special syntax considerations for aggregate
   functions are explained in <xref linkend="syntax-aggregates"/>.
   Consult <xref linkend="tutorial-agg"/> for additional introductory
   information.
  </para>

  <para>
   Aggregate functions that support <firstterm>Partial Mode</firstterm>
   are eligible to participate in various optimizations, such as parallel
   aggregation.
  </para>

  <para>
   While all aggregates below accept an optional
   <literal>ORDER BY</literal> clause (as outlined in <xref
   linkend="syntax-aggregates"/>), the clause has only been added to
   aggregates whose output is affected by ordering.
  </para>

   <table id="functions-aggregate-table">
    <title>General-Purpose Aggregate Functions</title>
    <tgroup cols="2">
     <colspec colname="col1" colwidth="10*"/>
     <colspec colname="col2" colwidth="1*"/>
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
       <entry>Partial Mode</entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>any_value</primary>
        </indexterm>
        <function>any_value</function> ( <type>anyelement</type> )
        <returnvalue><replaceable>same as input type</replaceable></returnvalue>
       </para>
       <para>
        Returns an arbitrary value from the non-null input values.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>array_agg</primary>
        </indexterm>
        <function>array_agg</function> ( <type>anynonarray</type> <literal>ORDER BY</literal> <literal>input_sort_columns</literal> )
        <returnvalue>anyarray</returnvalue>
       </para>
       <para>
        Collects all the input values, including nulls, into an array.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <function>array_agg</function> ( <type>anyarray</type> <literal>ORDER BY</literal> <literal>input_sort_columns</literal> )
        <returnvalue>anyarray</returnvalue>
       </para>
       <para>
        Concatenates all the input arrays into an array of one higher
        dimension.  (The inputs must all have the same dimensionality, and
        cannot be empty or null.)
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>average</primary>
        </indexterm>
        <indexterm>
         <primary>avg</primary>
        </indexterm>
        <function>avg</function> ( <type>smallint</type> )
        <returnvalue>numeric</returnvalue>
       </para>
       <para role="func_signature">
        <function>avg</function> ( <type>integer</type> )
        <returnvalue>numeric</returnvalue>
       </para>
       <para role="func_signature">
        <function>avg</function> ( <type>bigint</type> )
        <returnvalue>numeric</returnvalue>
       </para>
       <para role="func_signature">
        <function>avg</function> ( <type>numeric</type> )
        <returnvalue>numeric</returnvalue>
       </para>
       <para role="func_signature">
        <function>avg</function> ( <type>real</type> )
        <returnvalue>double precision</returnvalue>
       </para>
       <para role="func_signature">
        <function>avg</function> ( <type>double precision</type> )
        <returnvalue>double precision</returnvalue>
       </para>
       <para role="func_signature">
        <function>avg</function> ( <type>interval</type> )
        <returnvalue>interval</returnvalue>
       </para>
       <para>
        Computes the average (arithmetic mean) of all the non-null input
        values.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>bit_and</primary>
        </indexterm>
        <function>bit_and</function> ( <type>smallint</type> )
        <returnvalue>smallint</returnvalue>
       </para>
       <para role="func_signature">
        <function>bit_and</function> ( <type>integer</type> )
        <returnvalue>integer</returnvalue>
       </para>
       <para role="func_signature">
        <function>bit_and</function> ( <type>bigint</type> )
        <returnvalue>bigint</returnvalue>
       </para>
       <para role="func_signature">
        <function>bit_and</function> ( <type>bit</type> )
        <returnvalue>bit</returnvalue>
       </para>
       <para>
        Computes the bitwise AND of all non-null input values.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>bit_or</primary>
        </indexterm>
        <function>bit_or</function> ( <type>smallint</type> )
        <returnvalue>smallint</returnvalue>
       </para>
       <para role="func_signature">
        <function>bit_or</function> ( <type>integer</type> )
        <returnvalue>integer</returnvalue>
       </para>
       <para role="func_signature">
        <function>bit_or</function> ( <type>bigint</type> )
        <returnvalue>bigint</returnvalue>
       </para>
       <para role="func_signature">
        <function>bit_or</function> ( <type>bit</type> )
        <returnvalue>bit</returnvalue>
       </para>
       <para>
        Computes the bitwise OR of all non-null input values.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>bit_xor</primary>
        </indexterm>
        <function>bit_xor</function> ( <type>smallint</type> )
        <returnvalue>smallint</returnvalue>
       </para>
       <para role="func_signature">
        <function>bit_xor</function> ( <type>integer</type> )
        <returnvalue>integer</returnvalue>
       </para>
       <para role="func_signature">
        <function>bit_xor</function> ( <type>bigint</type> )
        <returnvalue>bigint</returnvalue>
       </para>
       <para role="func_signature">
        <function>bit_xor</function> ( <type>bit</type> )
        <returnvalue>bit</returnvalue>
       </para>
       <para>
        Computes the bitwise exclusive OR of all non-null input values.
        Can be useful as a checksum for an unordered set of values.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>bool_and</primary>
        </indexterm>
        <function>bool_and</function> ( <type>boolean</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Returns true if all non-null input values are true, otherwise false.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>bool_or</primary>
        </indexterm>
        <function>bool_or</function> ( <type>boolean</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Returns true if any non-null input value is true, otherwise false.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>count</primary>
        </indexterm>
        <function>count</function> ( <literal>*</literal> )
        <returnvalue>bigint</returnvalue>
       </para>
       <para>
        Computes the number of input rows.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <function>count</function> ( <type>"any"</type> )
        <returnvalue>bigint</returnvalue>
       </para>
       <para>
        Computes the number of input rows in which the input value is not
        null.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>every</primary>
        </indexterm>
        <function>every</function> ( <type>boolean</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        This is the SQL standard's equivalent to <function>bool_and</function>.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>json_agg</primary>
        </indexterm>
        <function>json_agg</function> ( <type>anyelement</type> <literal>ORDER BY</literal> <literal>input_sort_columns</literal> )
        <returnvalue>json</returnvalue>
       </para>
       <para role="func_signature">
        <indexterm>
         <primary>jsonb_agg</primary>
        </indexterm>
        <function>jsonb_agg</function> ( <type>anyelement</type> <literal>ORDER BY</literal> <literal>input_sort_columns</literal> )
        <returnvalue>jsonb</returnvalue>
       </para>
       <para>
        Collects all the input values, including nulls, into a JSON array.
        Values are converted to JSON as per <function>to_json</function>
        or <function>to_jsonb</function>.
       </para></entry>
       <entry>No</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>json_agg_strict</primary>
        </indexterm>
        <function>json_agg_strict</function> ( <type>anyelement</type> )
        <returnvalue>json</returnvalue>
       </para>
       <para role="func_signature">
        <indexterm>
         <primary>jsonb_agg_strict</primary>
        </indexterm>
        <function>jsonb_agg_strict</function> ( <type>anyelement</type> )
        <returnvalue>jsonb</returnvalue>
       </para>
       <para>
        Collects all the input values, skipping nulls, into a JSON array.
        Values are converted to JSON as per <function>to_json</function>
        or <function>to_jsonb</function>.
       </para></entry>
       <entry>No</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm><primary>json_arrayagg</primary></indexterm>
        <function>json_arrayagg</function> (
        <optional> <replaceable>value_expression</replaceable> </optional>
        <optional> <literal>ORDER BY</literal> <replaceable>sort_expression</replaceable> </optional>
        <optional> { <literal>NULL</literal> | <literal>ABSENT</literal> } <literal>ON NULL</literal> </optional>
        <optional> <literal>RETURNING</literal> <replaceable>data_type</replaceable> <optional> <literal>FORMAT JSON</literal> <optional> <literal>ENCODING UTF8</literal> </optional> </optional> </optional>)
       </para>
       <para>
        Behaves in the same way as <function>json_array</function>
        but as an aggregate function so it only takes one
        <replaceable>value_expression</replaceable> parameter.
        If <literal>ABSENT ON NULL</literal> is specified, any NULL
        values are omitted.
        If <literal>ORDER BY</literal> is specified, the elements will
        appear in the array in that order rather than in the input order.
       </para>
       <para>
        <literal>SELECT json_arrayagg(v) FROM (VALUES(2),(1)) t(v)</literal>
        <returnvalue>[2, 1]</returnvalue>
       </para></entry>
       <entry>No</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
         <indexterm><primary>json_objectagg</primary></indexterm>
         <function>json_objectagg</function> (
         <optional> { <replaceable>key_expression</replaceable> { <literal>VALUE</literal> | ':' } <replaceable>value_expression</replaceable> } </optional>
         <optional> { <literal>NULL</literal> | <literal>ABSENT</literal> } <literal>ON NULL</literal> </optional>
        <optional> { <literal>WITH</literal> | <literal>WITHOUT</literal> } <literal>UNIQUE</literal> <optional> <literal>KEYS</literal> </optional> </optional>
        <optional> <literal>RETURNING</literal> <replaceable>data_type</replaceable> <optional> <literal>FORMAT JSON</literal> <optional> <literal>ENCODING UTF8</literal> </optional> </optional> </optional>)
        </para>
        <para>
         Behaves like <function>json_object</function><!-- xref -->, but as an
         aggregate function, so it only takes one
         <replaceable>key_expression</replaceable> and one
         <replaceable>value_expression</replaceable> parameter.
        </para>
        <para>
         <literal>SELECT json_objectagg(k:v) FROM (VALUES ('a'::text,current_date),('b',current_date + 1)) AS t(k,v)</literal>
         <returnvalue>{ "a" : "2022-05-10", "b" : "2022-05-11" }</returnvalue>
       </para></entry>
       <entry>No</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>json_object_agg</primary>
        </indexterm>
        <function>json_object_agg</function> ( <parameter>key</parameter>
         <type>"any"</type>, <parameter>value</parameter>
         <type>"any"</type>
         <literal>ORDER BY</literal> <literal>input_sort_columns</literal> )
        <returnvalue>json</returnvalue>
       </para>
       <para role="func_signature">
        <indexterm>
         <primary>jsonb_object_agg</primary>
        </indexterm>
        <function>jsonb_object_agg</function> ( <parameter>key</parameter>
         <type>"any"</type>, <parameter>value</parameter>
         <type>"any"</type>
         <literal>ORDER BY</literal> <literal>input_sort_columns</literal> )
        <returnvalue>jsonb</returnvalue>
       </para>
       <para>
        Collects all the key/value pairs into a JSON object.  Key arguments
        are coerced to text; value arguments are converted as per
        <function>to_json</function> or <function>to_jsonb</function>.
        Values can be null, but keys cannot.
       </para></entry>
       <entry>No</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>json_object_agg_strict</primary>
        </indexterm>
        <function>json_object_agg_strict</function> (
         <parameter>key</parameter> <type>"any"</type>,
         <parameter>value</parameter> <type>"any"</type> )
        <returnvalue>json</returnvalue>
       </para>
       <para role="func_signature">
        <indexterm>
         <primary>jsonb_object_agg_strict</primary>
        </indexterm>
        <function>jsonb_object_agg_strict</function> (
         <parameter>key</parameter> <type>"any"</type>,
         <parameter>value</parameter> <type>"any"</type> )
        <returnvalue>jsonb</returnvalue>
       </para>
       <para>
        Collects all the key/value pairs into a JSON object.  Key arguments
        are coerced to text; value arguments are converted as per
        <function>to_json</function> or <function>to_jsonb</function>.
        The <parameter>key</parameter> cannot be null. If the
        <parameter>value</parameter> is null then the entry is skipped,
       </para></entry>
       <entry>No</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>json_object_agg_unique</primary>
        </indexterm>
        <function>json_object_agg_unique</function> (
         <parameter>key</parameter> <type>"any"</type>,
         <parameter>value</parameter> <type>"any"</type> )
        <returnvalue>json</returnvalue>
       </para>
       <para role="func_signature">
        <indexterm>
         <primary>jsonb_object_agg_unique</primary>
        </indexterm>
        <function>jsonb_object_agg_unique</function> (
         <parameter>key</parameter> <type>"any"</type>,
         <parameter>value</parameter> <type>"any"</type> )
        <returnvalue>jsonb</returnvalue>
       </para>
       <para>
        Collects all the key/value pairs into a JSON object.  Key arguments
        are coerced to text; value arguments are converted as per
        <function>to_json</function> or <function>to_jsonb</function>.
        Values can be null, but keys cannot.
        If there is a duplicate key an error is thrown.
       </para></entry>
       <entry>No</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>json_object_agg_unique_strict</primary>
        </indexterm>
        <function>json_object_agg_unique_strict</function> (
         <parameter>key</parameter> <type>"any"</type>,
         <parameter>value</parameter> <type>"any"</type> )
        <returnvalue>json</returnvalue>
       </para>
       <para role="func_signature">
        <indexterm>
         <primary>jsonb_object_agg_unique_strict</primary>
        </indexterm>
        <function>jsonb_object_agg_unique_strict</function> (
         <parameter>key</parameter> <type>"any"</type>,
         <parameter>value</parameter> <type>"any"</type> )
        <returnvalue>jsonb</returnvalue>
       </para>
       <para>
        Collects all the key/value pairs into a JSON object.  Key arguments
        are coerced to text; value arguments are converted as per
        <function>to_json</function> or <function>to_jsonb</function>.
        The <parameter>key</parameter> cannot be null. If the
        <parameter>value</parameter> is null then the entry is skipped.
        If there is a duplicate key an error is thrown.
       </para></entry>
       <entry>No</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>max</primary>
        </indexterm>
        <function>max</function> ( <replaceable>see text</replaceable> )
        <returnvalue><replaceable>same as input type</replaceable></returnvalue>
       </para>
       <para>
        Computes the maximum of the non-null input
        values.  Available for any numeric, string, date/time, or enum type,
        as well as <type>bytea</type>, <type>inet</type>, <type>interval</type>,
        <type>money</type>, <type>oid</type>, <type>oid8</type>,
        <type>pg_lsn</type>, <type>tid</type>, <type>uuid</type>,
        <type>xid8</type>,
        and also arrays and composite types containing sortable data types.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>min</primary>
        </indexterm>
        <function>min</function> ( <replaceable>see text</replaceable> )
        <returnvalue><replaceable>same as input type</replaceable></returnvalue>
       </para>
       <para>
        Computes the minimum of the non-null input
        values.  Available for any numeric, string, date/time, or enum type,
        as well as <type>bytea</type>, <type>inet</type>, <type>interval</type>,
        <type>money</type>, <type>oid</type>, <type>oid8</type>,
        <type>pg_lsn</type>, <type>tid</type>, <type>uuid</type>,
        <type>xid8</type>,
        and also arrays and composite types containing sortable data types.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>range_agg</primary>
        </indexterm>
        <function>range_agg</function> ( <parameter>value</parameter>
         <type>anyrange</type> )
        <returnvalue>anymultirange</returnvalue>
       </para>
       <para role="func_signature">
        <function>range_agg</function> ( <parameter>value</parameter>
         <type>anymultirange</type> )
        <returnvalue>anymultirange</returnvalue>
       </para>
       <para>
        Computes the union of the non-null input values.
       </para></entry>
       <entry>No</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>range_intersect_agg</primary>
        </indexterm>
        <function>range_intersect_agg</function> ( <parameter>value</parameter>
         <type>anyrange</type> )
        <returnvalue>anyrange</returnvalue>
       </para>
       <para role="func_signature">
        <function>range_intersect_agg</function> ( <parameter>value</parameter>
         <type>anymultirange</type> )
        <returnvalue>anymultirange</returnvalue>
       </para>
       <para>
        Computes the intersection of the non-null input values.
       </para></entry>
       <entry>No</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>string_agg</primary>
        </indexterm>
        <function>string_agg</function> ( <parameter>value</parameter>
         <type>text</type>, <parameter>delimiter</parameter> <type>text</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para role="func_signature">
        <function>string_agg</function> ( <parameter>value</parameter>
         <type>bytea</type>, <parameter>delimiter</parameter> <type>bytea</type>
         <literal>ORDER BY</literal> <literal>input_sort_columns</literal> )
        <returnvalue>bytea</returnvalue>
       </para>
       <para>
        Concatenates the non-null input values into a string.  Each value
        after the first is preceded by the
        corresponding <parameter>delimiter</parameter> (if it's not null).
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>sum</primary>
        </indexterm>
        <function>sum</function> ( <type>smallint</type> )
        <returnvalue>bigint</returnvalue>
       </para>
       <para role="func_signature">
        <function>sum</function> ( <type>integer</type> )
        <returnvalue>bigint</returnvalue>
       </para>
       <para role="func_signature">
        <function>sum</function> ( <type>bigint</type> )
        <returnvalue>numeric</returnvalue>
       </para>
       <para role="func_signature">
        <function>sum</function> ( <type>numeric</type> )
        <returnvalue>numeric</returnvalue>
       </para>
       <para role="func_signature">
        <function>sum</function> ( <type>real</type> )
        <returnvalue>real</returnvalue>
       </para>
       <para role="func_signature">
        <function>sum</function> ( <type>double precision</type> )
        <returnvalue>double precision</returnvalue>
       </para>
       <para role="func_signature">
        <function>sum</function> ( <type>interval</type> )
        <returnvalue>interval</returnvalue>
       </para>
       <para role="func_signature">
        <function>sum</function> ( <type>money</type> )
        <returnvalue>money</returnvalue>
       </para>
       <para>
        Computes the sum of the non-null input values.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>xmlagg</primary>
        </indexterm>
        <function>xmlagg</function> ( <type>xml</type> <literal>ORDER BY</literal> <literal>input_sort_columns</literal> )
        <returnvalue>xml</returnvalue>
       </para>
       <para>
        Concatenates the non-null XML input values (see
        <xref linkend="functions-xml-xmlagg"/>).
       </para></entry>
       <entry>No</entry>
      </row>
     </tbody>
    </tgroup>
   </table>

  <para>
   It should be noted that except for <function>count</function>,
   these functions return a null value when no rows are selected.  In
   particular, <function>sum</function> of no rows returns null, not
   zero as one might expect, and <function>array_agg</function>
   returns null rather than an empty array when there are no input
   rows.  The <function>coalesce</function> function can be used to
   substitute zero or an empty array for null when necessary.
  </para>

  <para>
   The aggregate functions <function>array_agg</function>,
   <function>json_agg</function>, <function>jsonb_agg</function>,
   <function>json_agg_strict</function>, <function>jsonb_agg_strict</function>,
   <function>json_object_agg</function>, <function>jsonb_object_agg</function>,
   <function>json_object_agg_strict</function>, <function>jsonb_object_agg_strict</function>,
   <function>json_object_agg_unique</function>, <function>jsonb_object_agg_unique</function>,
   <function>json_object_agg_unique_strict</function>,
   <function>jsonb_object_agg_unique_strict</function>,
   <function>string_agg</function>,
   and <function>xmlagg</function>, as well as similar user-defined
   aggregate functions, produce meaningfully different result values
   depending on the order of the input values.  This ordering is
   unspecified by default, but can be controlled by writing an
   <literal>ORDER BY</literal> clause within the aggregate call, as shown in
   <xref linkend="syntax-aggregates"/>.
   Alternatively, supplying the input values from a sorted subquery
   will usually work.  For example:

<screen><![CDATA[
SELECT xmlagg(x) FROM (SELECT x FROM test ORDER BY y DESC) AS tab;
]]></screen>

   Beware that this approach can fail if the outer query level contains
   additional processing, such as a join, because that might cause the
   subquery's output to be reordered before the aggregate is computed.
  </para>

  <note>
    <indexterm>
      <primary>ANY</primary>
    </indexterm>
    <indexterm>
      <primary>SOME</primary>
    </indexterm>
    <para>
      The boolean aggregates <function>bool_and</function> and
      <function>bool_or</function> correspond to the standard SQL aggregates
      <function>every</function> and <function>any</function> or
      <function>some</function>.
      <productname>PostgreSQL</productname>
      supports <function>every</function>, but not <function>any</function>
      or <function>some</function>, because there is an ambiguity built into
      the standard syntax:
<programlisting>
SELECT b1 = ANY((SELECT b2 FROM t2 ...)) FROM t1 ...;
</programlisting>
      Here <function>ANY</function> can be considered either as introducing
      a subquery, or as being an aggregate function, if the subquery
      returns one row with a Boolean value.
      Thus the standard name cannot be given to these aggregates.
    </para>
  </note>

  <note>
   <para>
    Users accustomed to working with other SQL database management
    systems might be disappointed by the performance of the
    <function>count</function> aggregate when it is applied to the
    entire table. A query like:
<programlisting>
SELECT count(*) FROM sometable;
</programlisting>
    will require effort proportional to the size of the table:
    <productname>PostgreSQL</productname> will need to scan either the
    entire table or the entirety of an index that includes all rows in
    the table.
   </para>
  </note>

  <para>
   <xref linkend="functions-aggregate-statistics-table"/> shows
   aggregate functions typically used in statistical analysis.
   (These are separated out merely to avoid cluttering the listing
   of more-commonly-used aggregates.)  Functions shown as
   accepting <replaceable>numeric_type</replaceable> are available for all
   the types <type>smallint</type>, <type>integer</type>,
   <type>bigint</type>, <type>numeric</type>, <type>real</type>,
   and <type>double precision</type>.
   Where the description mentions
   <parameter>N</parameter>, it means the
   number of input rows for which all the input expressions are non-null.
   In all cases, null is returned if the computation is meaningless,
   for example when <parameter>N</parameter> is zero.
  </para>

  <indexterm>
   <primary>statistics</primary>
  </indexterm>
  <indexterm>
   <primary>linear regression</primary>
  </indexterm>

   <table id="functions-aggregate-statistics-table">
    <title>Aggregate Functions for Statistics</title>
    <tgroup cols="2">
     <colspec colname="col1" colwidth="10*"/>
     <colspec colname="col2" colwidth="1*"/>
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
       <entry>Partial Mode</entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>correlation</primary>
        </indexterm>
        <indexterm>
         <primary>corr</primary>
        </indexterm>
        <function>corr</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
        <returnvalue>double precision</returnvalue>
       </para>
       <para>
        Computes the correlation coefficient.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>covariance</primary>
         <secondary>population</secondary>
        </indexterm>
        <indexterm>
         <primary>covar_pop</primary>
        </indexterm>
        <function>covar_pop</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
        <returnvalue>double precision</returnvalue>
       </para>
       <para>
        Computes the population covariance.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>covariance</primary>
         <secondary>sample</secondary>
        </indexterm>
        <indexterm>
         <primary>covar_samp</primary>
        </indexterm>
        <function>covar_samp</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
        <returnvalue>double precision</returnvalue>
       </para>
       <para>
        Computes the sample covariance.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>regr_avgx</primary>
        </indexterm>
        <function>regr_avgx</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
        <returnvalue>double precision</returnvalue>
       </para>
       <para>
        Computes the average of the independent variable,
        <literal>sum(<parameter>X</parameter>)/<parameter>N</parameter></literal>.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>regr_avgy</primary>
        </indexterm>
        <function>regr_avgy</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
        <returnvalue>double precision</returnvalue>
       </para>
       <para>
        Computes the average of the dependent variable,
        <literal>sum(<parameter>Y</parameter>)/<parameter>N</parameter></literal>.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>regr_count</primary>
        </indexterm>
        <function>regr_count</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
        <returnvalue>bigint</returnvalue>
       </para>
       <para>
        Computes the number of rows in which both inputs are non-null.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>regression intercept</primary>
        </indexterm>
        <indexterm>
         <primary>regr_intercept</primary>
        </indexterm>
        <function>regr_intercept</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
        <returnvalue>double precision</returnvalue>
       </para>
       <para>
        Computes the y-intercept of the least-squares-fit linear equation
        determined by the
        (<parameter>X</parameter>, <parameter>Y</parameter>) pairs.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>regr_r2</primary>
        </indexterm>
        <function>regr_r2</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
        <returnvalue>double precision</returnvalue>
       </para>
       <para>
        Computes the square of the correlation coefficient.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>regression slope</primary>
        </indexterm>
        <indexterm>
         <primary>regr_slope</primary>
        </indexterm>
        <function>regr_slope</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
        <returnvalue>double precision</returnvalue>
       </para>
       <para>
        Computes the slope of the least-squares-fit linear equation determined
        by the (<parameter>X</parameter>, <parameter>Y</parameter>)
        pairs.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>regr_sxx</primary>
        </indexterm>
        <function>regr_sxx</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
        <returnvalue>double precision</returnvalue>
       </para>
       <para>
        Computes the <quote>sum of squares</quote> of the independent
        variable,
        <literal>sum(<parameter>X</parameter>^2) - sum(<parameter>X</parameter>)^2/<parameter>N</parameter></literal>.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>regr_sxy</primary>
        </indexterm>
        <function>regr_sxy</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
        <returnvalue>double precision</returnvalue>
       </para>
       <para>
        Computes the <quote>sum of products</quote> of independent times
        dependent variables,
        <literal>sum(<parameter>X</parameter>*<parameter>Y</parameter>) - sum(<parameter>X</parameter>) * sum(<parameter>Y</parameter>)/<parameter>N</parameter></literal>.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>regr_syy</primary>
        </indexterm>
        <function>regr_syy</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
        <returnvalue>double precision</returnvalue>
       </para>
       <para>
        Computes the <quote>sum of squares</quote> of the dependent
        variable,
        <literal>sum(<parameter>Y</parameter>^2) - sum(<parameter>Y</parameter>)^2/<parameter>N</parameter></literal>.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>standard deviation</primary>
        </indexterm>
        <indexterm>
         <primary>stddev</primary>
        </indexterm>
        <function>stddev</function> ( <replaceable>numeric_type</replaceable> )
        <returnvalue></returnvalue> <type>double precision</type>
        for <type>real</type> or <type>double precision</type>,
        otherwise <type>numeric</type>
       </para>
       <para>
        This is a historical alias for <function>stddev_samp</function>.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>standard deviation</primary>
         <secondary>population</secondary>
        </indexterm>
        <indexterm>
         <primary>stddev_pop</primary>
        </indexterm>
        <function>stddev_pop</function> ( <replaceable>numeric_type</replaceable> )
        <returnvalue></returnvalue> <type>double precision</type>
        for <type>real</type> or <type>double precision</type>,
        otherwise <type>numeric</type>
       </para>
       <para>
        Computes the population standard deviation of the input values.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>standard deviation</primary>
         <secondary>sample</secondary>
        </indexterm>
        <indexterm>
         <primary>stddev_samp</primary>
        </indexterm>
        <function>stddev_samp</function> ( <replaceable>numeric_type</replaceable> )
        <returnvalue></returnvalue> <type>double precision</type>
        for <type>real</type> or <type>double precision</type>,
        otherwise <type>numeric</type>
       </para>
       <para>
        Computes the sample standard deviation of the input values.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>variance</primary>
        </indexterm>
        <function>variance</function> ( <replaceable>numeric_type</replaceable> )
        <returnvalue></returnvalue> <type>double precision</type>
        for <type>real</type> or <type>double precision</type>,
        otherwise <type>numeric</type>
       </para>
       <para>
        This is a historical alias for <function>var_samp</function>.
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>variance</primary>
         <secondary>population</secondary>
        </indexterm>
        <indexterm>
         <primary>var_pop</primary>
        </indexterm>
        <function>var_pop</function> ( <replaceable>numeric_type</replaceable> )
        <returnvalue></returnvalue> <type>double precision</type>
        for <type>real</type> or <type>double precision</type>,
        otherwise <type>numeric</type>
       </para>
       <para>
        Computes the population variance of the input values (square of the
        population standard deviation).
       </para></entry>
       <entry>Yes</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>variance</primary>
         <secondary>sample</secondary>
        </indexterm>
        <indexterm>
         <primary>var_samp</primary>
        </indexterm>
        <function>var_samp</function> ( <replaceable>numeric_type</replaceable> )
        <returnvalue></returnvalue> <type>double precision</type>
        for <type>real</type> or <type>double precision</type>,
        otherwise <type>numeric</type>
       </para>
       <para>
        Computes the sample variance of the input values (square of the sample
        standard deviation).
       </para></entry>
       <entry>Yes</entry>
      </row>
     </tbody>
    </tgroup>
   </table>

  <para>
   <xref linkend="functions-orderedset-table"/> shows some
   aggregate functions that use the <firstterm>ordered-set aggregate</firstterm>
   syntax.  These functions are sometimes referred to as <quote>inverse
   distribution</quote> functions.  Their aggregated input is introduced by
   <literal>ORDER BY</literal>, and they may also take a <firstterm>direct
   argument</firstterm> that is not aggregated, but is computed only once.
   All these functions ignore null values in their aggregated input.
   For those that take a <parameter>fraction</parameter> parameter, the
   fraction value must be between 0 and 1; an error is thrown if not.
   However, a null <parameter>fraction</parameter> value simply produces a
   null result.
  </para>

  <indexterm>
   <primary>ordered-set aggregate</primary>
   <secondary>built-in</secondary>
  </indexterm>
  <indexterm>
   <primary>inverse distribution</primary>
  </indexterm>

   <table id="functions-orderedset-table">
    <title>Ordered-Set Aggregate Functions</title>
    <tgroup cols="2">
     <colspec colname="col1" colwidth="10*"/>
     <colspec colname="col2" colwidth="1*"/>
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
       <entry>Partial Mode</entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>mode</primary>
         <secondary>statistical</secondary>
        </indexterm>
        <function>mode</function> () <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <type>anyelement</type> )
        <returnvalue>anyelement</returnvalue>
       </para>
       <para>
        Computes the <firstterm>mode</firstterm>, the most frequent
        value of the aggregated argument (arbitrarily choosing the first one
        if there are multiple equally-frequent values).  The aggregated
        argument must be of a sortable type.
       </para></entry>
       <entry>No</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>percentile</primary>
         <secondary>continuous</secondary>
        </indexterm>
        <function>percentile_cont</function> ( <parameter>fraction</parameter> <type>double precision</type> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <type>double precision</type> )
        <returnvalue>double precision</returnvalue>
       </para>
       <para role="func_signature">
        <function>percentile_cont</function> ( <parameter>fraction</parameter> <type>double precision</type> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <type>interval</type> )
        <returnvalue>interval</returnvalue>
       </para>
       <para>
        Computes the <firstterm>continuous percentile</firstterm>, a value
        corresponding to the specified <parameter>fraction</parameter>
        within the ordered set of aggregated argument values.  This will
        interpolate between adjacent input items if needed.
       </para></entry>
       <entry>No</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <function>percentile_cont</function> ( <parameter>fractions</parameter> <type>double precision[]</type> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <type>double precision</type> )
        <returnvalue>double precision[]</returnvalue>
       </para>
       <para role="func_signature">
        <function>percentile_cont</function> ( <parameter>fractions</parameter> <type>double precision[]</type> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <type>interval</type> )
        <returnvalue>interval[]</returnvalue>
       </para>
       <para>
        Computes multiple continuous percentiles.  The result is an array of
        the same dimensions as the <parameter>fractions</parameter>
        parameter, with each non-null element replaced by the (possibly
        interpolated) value corresponding to that percentile.
       </para></entry>
       <entry>No</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>percentile</primary>
         <secondary>discrete</secondary>
        </indexterm>
        <function>percentile_disc</function> ( <parameter>fraction</parameter> <type>double precision</type> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <type>anyelement</type> )
        <returnvalue>anyelement</returnvalue>
       </para>
       <para>
        Computes the <firstterm>discrete percentile</firstterm>, the first
        value within the ordered set of aggregated argument values whose
        position in the ordering equals or exceeds the
        specified <parameter>fraction</parameter>.  The aggregated
        argument must be of a sortable type.
       </para></entry>
       <entry>No</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <function>percentile_disc</function> ( <parameter>fractions</parameter> <type>double precision[]</type> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <type>anyelement</type> )
        <returnvalue>anyarray</returnvalue>
       </para>
       <para>
        Computes multiple discrete percentiles.  The result is an array of the
        same dimensions as the <parameter>fractions</parameter> parameter,
        with each non-null element replaced by the input value corresponding
        to that percentile.
        The aggregated argument must be of a sortable type.
       </para></entry>
       <entry>No</entry>
      </row>
     </tbody>
    </tgroup>
   </table>

  <indexterm>
   <primary>hypothetical-set aggregate</primary>
   <secondary>built-in</secondary>
  </indexterm>

  <para>
   Each of the <quote>hypothetical-set</quote> aggregates listed in
   <xref linkend="functions-hypothetical-table"/> is associated with a
   window function of the same name defined in
   <xref linkend="functions-window"/>.  In each case, the aggregate's result
   is the value that the associated window function would have
   returned for the <quote>hypothetical</quote> row constructed from
   <replaceable>args</replaceable>, if such a row had been added to the sorted
   group of rows represented by the <replaceable>sorted_args</replaceable>.
   For each of these functions, the list of direct arguments
   given in <replaceable>args</replaceable> must match the number and types of
   the aggregated arguments given in <replaceable>sorted_args</replaceable>.
   Unlike most built-in aggregates, these aggregates are not strict, that is
   they do not drop input rows containing nulls.  Null values sort according
   to the rule specified in the <literal>ORDER BY</literal> clause.
  </para>

   <table id="functions-hypothetical-table">
    <title>Hypothetical-Set Aggregate Functions</title>
    <tgroup cols="2">
     <colspec colname="col1" colwidth="10*"/>
     <colspec colname="col2" colwidth="1*"/>
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
       <entry>Partial Mode</entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>rank</primary>
         <secondary>hypothetical</secondary>
        </indexterm>
        <function>rank</function> ( <replaceable>args</replaceable> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <replaceable>sorted_args</replaceable> )
        <returnvalue>bigint</returnvalue>
       </para>
       <para>
        Computes the rank of the hypothetical row, with gaps; that is, the row
        number of the first row in its peer group.
       </para></entry>
       <entry>No</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>dense_rank</primary>
         <secondary>hypothetical</secondary>
        </indexterm>
        <function>dense_rank</function> ( <replaceable>args</replaceable> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <replaceable>sorted_args</replaceable> )
        <returnvalue>bigint</returnvalue>
       </para>
       <para>
        Computes the rank of the hypothetical row, without gaps; this function
        effectively counts peer groups.
       </para></entry>
       <entry>No</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>percent_rank</primary>
         <secondary>hypothetical</secondary>
        </indexterm>
        <function>percent_rank</function> ( <replaceable>args</replaceable> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <replaceable>sorted_args</replaceable> )
        <returnvalue>double precision</returnvalue>
       </para>
       <para>
        Computes the relative rank of the hypothetical row, that is
        (<function>rank</function> - 1) / (total rows - 1).
        The value thus ranges from 0 to 1 inclusive.
       </para></entry>
       <entry>No</entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>cume_dist</primary>
         <secondary>hypothetical</secondary>
        </indexterm>
        <function>cume_dist</function> ( <replaceable>args</replaceable> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <replaceable>sorted_args</replaceable> )
        <returnvalue>double precision</returnvalue>
       </para>
       <para>
        Computes the cumulative distribution, that is (number of rows
        preceding or peers with hypothetical row) / (total rows).  The value
        thus ranges from 1/<parameter>N</parameter> to 1.
       </para></entry>
       <entry>No</entry>
      </row>
     </tbody>
    </tgroup>
   </table>

  <table id="functions-grouping-table">
   <title>Grouping Operations</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>GROUPING</primary>
        </indexterm>
        <function>GROUPING</function> ( <replaceable>group_by_expression(s)</replaceable> )
        <returnvalue>integer</returnvalue>
       </para>
       <para>
        Returns a bit mask indicating which <literal>GROUP BY</literal>
        expressions are not included in the current grouping set.
        Bits are assigned with the rightmost argument corresponding to the
        least-significant bit; each bit is 0 if the corresponding expression
        is included in the grouping criteria of the grouping set generating
        the current result row, and 1 if it is not included.
       </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

   <para>
    The grouping operations shown in
    <xref linkend="functions-grouping-table"/> are used in conjunction with
    grouping sets (see <xref linkend="queries-grouping-sets"/>) to distinguish
    result rows.  The arguments to the <literal>GROUPING</literal> function
    are not actually evaluated, but they must exactly match expressions given
    in the <literal>GROUP BY</literal> clause of the associated query level.
    For example:
<screen>
<prompt>=&gt;</prompt> <userinput>SELECT * FROM items_sold;</userinput>
 make  | model | sales
-------+-------+-------
 Foo   | GT    |  10
 Foo   | Tour  |  20
 Bar   | City  |  15
 Bar   | Sport |  5
(4 rows)

<prompt>=&gt;</prompt> <userinput>SELECT make, model, GROUPING(make,model), sum(sales) FROM items_sold GROUP BY ROLLUP(make,model);</userinput>
 make  | model | grouping | sum
-------+-------+----------+-----
 Foo   | GT    |        0 | 10
 Foo   | Tour  |        0 | 20
 Bar   | City  |        0 | 15
 Bar   | Sport |        0 | 5
 Foo   |       |        1 | 30
 Bar   |       |        1 | 20
       |       |        3 | 50
(7 rows)
</screen>
    Here, the <literal>grouping</literal> value <literal>0</literal> in the
    first four rows shows that those have been grouped normally, over both the
    grouping columns.  The value <literal>1</literal> indicates
    that <literal>model</literal> was not grouped by in the next-to-last two
    rows, and the value <literal>3</literal> indicates that
    neither <literal>make</literal> nor <literal>model</literal> was grouped
    by in the last row (which therefore is an aggregate over all the input
    rows).
   </para>

 </sect1>