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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>7.5. Sorting Rows (ORDER BY)</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="queries-union.html" title="7.4. Combining Queries (UNION, INTERSECT, EXCEPT)" /><link rel="next" href="queries-limit.html" title="7.6. LIMIT and OFFSET" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">7.5. Sorting Rows (<code class="literal">ORDER BY</code>)</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="queries-union.html" title="7.4. Combining Queries (UNION, INTERSECT, EXCEPT)">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="queries.html" title="Chapter 7. Queries">Up</a></td><th width="60%" align="center">Chapter 7. Queries</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="queries-limit.html" title="7.6. LIMIT and OFFSET">Next</a></td></tr></table><hr /></div><div class="sect1" id="QUERIES-ORDER"><div class="titlepage"><div><div><h2 class="title" style="clear: both">7.5. Sorting Rows (<code class="literal">ORDER BY</code>)</h2></div></div></div><a id="id-1.5.6.9.2" class="indexterm"></a><a id="id-1.5.6.9.3" class="indexterm"></a><p>
   After a query has produced an output table (after the select list
   has been processed) it can optionally be sorted.  If sorting is not
   chosen, the rows will be returned in an unspecified order.  The actual
   order in that case will depend on the scan and join plan types and
   the order on disk, but it must not be relied on.  A particular
   output ordering can only be guaranteed if the sort step is explicitly
   chosen.
  </p><p>
   The <code class="literal">ORDER BY</code> clause specifies the sort order:
</p><pre class="synopsis">
SELECT <em class="replaceable"><code>select_list</code></em>
    FROM <em class="replaceable"><code>table_expression</code></em>
    ORDER BY <em class="replaceable"><code>sort_expression1</code></em> [<span class="optional">ASC | DESC</span>] [<span class="optional">NULLS { FIRST | LAST }</span>]
             [<span class="optional">, <em class="replaceable"><code>sort_expression2</code></em> [<span class="optional">ASC | DESC</span>] [<span class="optional">NULLS { FIRST | LAST }</span>] ...</span>]
</pre><p>
   The sort expression(s) can be any expression that would be valid in the
   query's select list.  An example is:
</p><pre class="programlisting">
SELECT a, b FROM table1 ORDER BY a + b, c;
</pre><p>
   When more than one expression is specified,
   the later values are used to sort rows that are equal according to the
   earlier values.  Each expression can be followed by an optional
   <code class="literal">ASC</code> or <code class="literal">DESC</code> keyword to set the sort direction to
   ascending or descending.  <code class="literal">ASC</code> order is the default.
   Ascending order puts smaller values first, where
   <span class="quote"><span class="quote">smaller</span></span> is defined in terms of the
   <code class="literal">&lt;</code> operator.  Similarly, descending order is
   determined with the <code class="literal">&gt;</code> operator.
    <a href="#ftn.id-1.5.6.9.5.10" class="footnote"><sup class="footnote" id="id-1.5.6.9.5.10">[6]</sup></a>
  </p><p>
   The <code class="literal">NULLS FIRST</code> and <code class="literal">NULLS LAST</code> options can be
   used to determine whether nulls appear before or after non-null values
   in the sort ordering.  By default, null values sort as if larger than any
   non-null value; that is, <code class="literal">NULLS FIRST</code> is the default for
   <code class="literal">DESC</code> order, and <code class="literal">NULLS LAST</code> otherwise.
  </p><p>
   Note that the ordering options are considered independently for each
   sort column.  For example <code class="literal">ORDER BY x, y DESC</code> means
   <code class="literal">ORDER BY x ASC, y DESC</code>, which is not the same as
   <code class="literal">ORDER BY x DESC, y DESC</code>.
  </p><p>
   A <em class="replaceable"><code>sort_expression</code></em> can also be the column label or number
   of an output column, as in:
</p><pre class="programlisting">
SELECT a + b AS sum, c FROM table1 ORDER BY sum;
SELECT a, max(b) FROM table1 GROUP BY a ORDER BY 1;
</pre><p>
   both of which sort by the first output column.  Note that an output
   column name has to stand alone, that is, it cannot be used in an expression
   — for example, this is <span class="emphasis"><em>not</em></span> correct:
</p><pre class="programlisting">
SELECT a + b AS sum, c FROM table1 ORDER BY sum + c;          -- wrong
</pre><p>
   This restriction is made to reduce ambiguity.  There is still
   ambiguity if an <code class="literal">ORDER BY</code> item is a simple name that
   could match either an output column name or a column from the table
   expression.  The output column is used in such cases.  This would
   only cause confusion if you use <code class="literal">AS</code> to rename an output
   column to match some other table column's name.
  </p><p>
   <code class="literal">ORDER BY</code> can be applied to the result of a
   <code class="literal">UNION</code>, <code class="literal">INTERSECT</code>, or <code class="literal">EXCEPT</code>
   combination, but in this case it is only permitted to sort by
   output column names or numbers, not by expressions.
  </p><div class="footnotes"><br /><hr style="width:100; text-align:left;margin-left: 0" /><div id="ftn.id-1.5.6.9.5.10" class="footnote"><p><a href="#id-1.5.6.9.5.10" class="para"><sup class="para">[6] </sup></a>
      Actually, <span class="productname">PostgreSQL</span> uses the <em class="firstterm">default B-tree
      operator class</em> for the expression's data type to determine the sort
      ordering for <code class="literal">ASC</code> and <code class="literal">DESC</code>.  Conventionally,
      data types will be set up so that the <code class="literal">&lt;</code> and
      <code class="literal">&gt;</code> operators correspond to this sort ordering,
      but a user-defined data type's designer could choose to do something
      different.
     </p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="queries-union.html" title="7.4. Combining Queries (UNION, INTERSECT, EXCEPT)">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="queries.html" title="Chapter 7. Queries">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="queries-limit.html" title="7.6. LIMIT and OFFSET">Next</a></td></tr><tr><td width="40%" align="left" valign="top">7.4. Combining Queries (<code class="literal">UNION</code>, <code class="literal">INTERSECT</code>, <code class="literal">EXCEPT</code></td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 7.6. <code class="literal">LIMIT</code> and <code class="literal">OFFSET</code></td></tr></table></div></body></html>