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| author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-05-04 12:15:05 +0000 |
|---|---|---|
| committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-05-04 12:15:05 +0000 |
| commit | 46651ce6fe013220ed397add242004d764fc0153 (patch) | |
| tree | 6e5299f990f88e60174a1d3ae6e48eedd2688b2b /doc/src/sgml/html/tsm-system-rows.html | |
| parent | Initial commit. (diff) | |
| download | postgresql-14-upstream.tar.xz postgresql-14-upstream.zip | |
Adding upstream version 14.5.upstream/14.5upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'doc/src/sgml/html/tsm-system-rows.html')
| -rw-r--r-- | doc/src/sgml/html/tsm-system-rows.html | 39 |
1 files changed, 39 insertions, 0 deletions
diff --git a/doc/src/sgml/html/tsm-system-rows.html b/doc/src/sgml/html/tsm-system-rows.html new file mode 100644 index 0000000..5d88f97 --- /dev/null +++ b/doc/src/sgml/html/tsm-system-rows.html @@ -0,0 +1,39 @@ +<?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>F.43. tsm_system_rows</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="test-decoding.html" title="F.42. test_decoding" /><link rel="next" href="tsm-system-time.html" title="F.44. tsm_system_time" /></head><body id="docContent" class="container-fluid col-10"><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">F.43. tsm_system_rows</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="test-decoding.html" title="F.42. test_decoding">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules">Up</a></td><th width="60%" align="center">Appendix F. Additional Supplied Modules</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 14.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="tsm-system-time.html" title="F.44. tsm_system_time">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="TSM-SYSTEM-ROWS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.43. tsm_system_rows</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="tsm-system-rows.html#id-1.11.7.52.8">F.43.1. Examples</a></span></dt></dl></div><a id="id-1.11.7.52.2" class="indexterm"></a><p> + The <code class="filename">tsm_system_rows</code> module provides the table sampling method + <code class="literal">SYSTEM_ROWS</code>, which can be used in + the <code class="literal">TABLESAMPLE</code> clause of a <a class="link" href="sql-select.html" title="SELECT"><code class="command">SELECT</code></a> + command. + </p><p> + This table sampling method accepts a single integer argument that is the + maximum number of rows to read. The resulting sample will always contain + exactly that many rows, unless the table does not contain enough rows, in + which case the whole table is selected. + </p><p> + Like the built-in <code class="literal">SYSTEM</code> sampling + method, <code class="literal">SYSTEM_ROWS</code> performs block-level sampling, so + that the sample is not completely random but may be subject to clustering + effects, especially if only a small number of rows are requested. + </p><p> + <code class="literal">SYSTEM_ROWS</code> does not support + the <code class="literal">REPEATABLE</code> clause. + </p><p> + This module is considered <span class="quote">“<span class="quote">trusted</span>”</span>, that is, it can be + installed by non-superusers who have <code class="literal">CREATE</code> privilege + on the current database. + </p><div class="sect2" id="id-1.11.7.52.8"><div class="titlepage"><div><div><h3 class="title">F.43.1. Examples</h3></div></div></div><p> + Here is an example of selecting a sample of a table with + <code class="literal">SYSTEM_ROWS</code>. First install the extension: + </p><pre class="programlisting"> +CREATE EXTENSION tsm_system_rows; +</pre><p> + Then you can use it in a <code class="command">SELECT</code> command, for instance: + +</p><pre class="programlisting"> +SELECT * FROM my_table TABLESAMPLE SYSTEM_ROWS(100); +</pre><p> + </p><p> + This command will return a sample of 100 rows from the + table <code class="structname">my_table</code> (unless the table does not have 100 + visible rows, in which case all its rows are returned). + </p></div></div><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="test-decoding.html" title="F.42. test_decoding">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="tsm-system-time.html" title="F.44. tsm_system_time">Next</a></td></tr><tr><td width="40%" align="left" valign="top">F.42. test_decoding </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 14.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> F.44. tsm_system_time</td></tr></table></div></body></html>
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