<!-- doc/src/sgml/tsm-system-rows.sgml -->

<sect1 id="tsm-system-rows" xreflabel="tsm_system_rows">

<title>tsm_system_rows</title>

<indexterm zone="tsm-system-rows">

<primary>tsm_system_rows</primary>

</indexterm>

<para>

The <filename>tsm_system_rows</> module provides the tablesample method

<literal>SYSTEM_ROWS</literal>, which can be used inside the

<command>TABLESAMPLE</command> clause of a <command>SELECT</command>.

</para>

<para>

This tablesample method uses a linear probing algorithm to read sample

of a table and uses actual number of rows as limit (unlike the

<literal>SYSTEM</literal> tablesample method which limits by percentage

of a table).

</para>

<sect2>

<title>Examples</title>

<para>

Here is an example of selecting sample of a table with

<literal>SYSTEM_ROWS</>. First install the extension:

</para>

<programlisting>

CREATE EXTENSION tsm_system_rows;

</programlisting>

<para>

Then you can use it in <command>SELECT</command> command same way as other

tablesample methods:

<programlisting>

SELECT * FROM my_table TABLESAMPLE SYSTEM_ROWS(100);

</programlisting>

</para>

<para>

The above command will return a sample of 100 rows from the table my_table

(less if the table does not have 100 visible rows).

</para>

</sect2>

</sect1>