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| author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-16 19:46:48 +0000 |
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| committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-16 19:46:48 +0000 |
| commit | 311bcfc6b3acdd6fd152798c7f287ddf74fa2a98 (patch) | |
| tree | 0ec307299b1dada3701e42f4ca6eda57d708261e /doc/src/sgml/html/queries-limit.html | |
| parent | Initial commit. (diff) | |
| download | postgresql-15-311bcfc6b3acdd6fd152798c7f287ddf74fa2a98.tar.xz postgresql-15-311bcfc6b3acdd6fd152798c7f287ddf74fa2a98.zip | |
Adding upstream version 15.4.upstream/15.4upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'doc/src/sgml/html/queries-limit.html')
| -rw-r--r-- | doc/src/sgml/html/queries-limit.html | 48 |
1 files changed, 48 insertions, 0 deletions
diff --git a/doc/src/sgml/html/queries-limit.html b/doc/src/sgml/html/queries-limit.html new file mode 100644 index 0000000..4236145 --- /dev/null +++ b/doc/src/sgml/html/queries-limit.html @@ -0,0 +1,48 @@ +<?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>7.6. LIMIT and OFFSET</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-order.html" title="7.5. Sorting Rows (ORDER BY)" /><link rel="next" href="queries-values.html" title="7.7. VALUES Lists" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">7.6. <code class="literal">LIMIT</code> and <code class="literal">OFFSET</code></th></tr><tr><td width="10%" align="left"><a accesskey="p" href="queries-order.html" title="7.5. Sorting Rows (ORDER BY)">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 15.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="queries-values.html" title="7.7. VALUES Lists">Next</a></td></tr></table><hr /></div><div class="sect1" id="QUERIES-LIMIT"><div class="titlepage"><div><div><h2 class="title" style="clear: both">7.6. <code class="literal">LIMIT</code> and <code class="literal">OFFSET</code></h2></div></div></div><a id="id-1.5.6.10.2" class="indexterm"></a><a id="id-1.5.6.10.3" class="indexterm"></a><p> + <code class="literal">LIMIT</code> and <code class="literal">OFFSET</code> allow you to retrieve just + a portion of the rows that are generated by the rest of the query: +</p><pre class="synopsis"> +SELECT <em class="replaceable"><code>select_list</code></em> + FROM <em class="replaceable"><code>table_expression</code></em> + [<span class="optional"> ORDER BY ... </span>] + [<span class="optional"> LIMIT { <em class="replaceable"><code>number</code></em> | ALL } </span>] [<span class="optional"> OFFSET <em class="replaceable"><code>number</code></em> </span>] +</pre><p> + </p><p> + If a limit count is given, no more than that many rows will be + returned (but possibly fewer, if the query itself yields fewer rows). + <code class="literal">LIMIT ALL</code> is the same as omitting the <code class="literal">LIMIT</code> + clause, as is <code class="literal">LIMIT</code> with a NULL argument. + </p><p> + <code class="literal">OFFSET</code> says to skip that many rows before beginning to + return rows. <code class="literal">OFFSET 0</code> is the same as omitting the + <code class="literal">OFFSET</code> clause, as is <code class="literal">OFFSET</code> with a NULL argument. + </p><p> + If both <code class="literal">OFFSET</code> + and <code class="literal">LIMIT</code> appear, then <code class="literal">OFFSET</code> rows are + skipped before starting to count the <code class="literal">LIMIT</code> rows that + are returned. + </p><p> + When using <code class="literal">LIMIT</code>, it is important to use an + <code class="literal">ORDER BY</code> clause that constrains the result rows into a + unique order. Otherwise you will get an unpredictable subset of + the query's rows. You might be asking for the tenth through + twentieth rows, but tenth through twentieth in what ordering? The + ordering is unknown, unless you specified <code class="literal">ORDER BY</code>. + </p><p> + The query optimizer takes <code class="literal">LIMIT</code> into account when + generating query plans, so you are very likely to get different + plans (yielding different row orders) depending on what you give + for <code class="literal">LIMIT</code> and <code class="literal">OFFSET</code>. Thus, using + different <code class="literal">LIMIT</code>/<code class="literal">OFFSET</code> values to select + different subsets of a query result <span class="emphasis"><em>will give + inconsistent results</em></span> unless you enforce a predictable + result ordering with <code class="literal">ORDER BY</code>. This is not a bug; it + is an inherent consequence of the fact that SQL does not promise to + deliver the results of a query in any particular order unless + <code class="literal">ORDER BY</code> is used to constrain the order. + </p><p> + The rows skipped by an <code class="literal">OFFSET</code> clause still have to be + computed inside the server; therefore a large <code class="literal">OFFSET</code> + might be inefficient. + </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="queries-order.html" title="7.5. Sorting Rows (ORDER BY)">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-values.html" title="7.7. VALUES Lists">Next</a></td></tr><tr><td width="40%" align="left" valign="top">7.5. Sorting Rows (<code class="literal">ORDER BY</code>) </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.4 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 7.7. <code class="literal">VALUES</code> Lists</td></tr></table></div></body></html>
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