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Doc: clarify behavior of row-limit arguments in the PLs' SPI wrappers.

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plperl, plpython, and pltcl all provide query-execution functions
that are thin wrappers around SPI_execute() or its variants.
The SPI functions document their row-count limit arguments clearly,
as "maximum number of rows to return, or 0 for no limit".  However
the PLs' documentation failed to explain this special behavior of
zero, so that a reader might well assume it means "fetch zero
rows".  Improve that.

Daniel Gustafsson and Tom Lane, per report from Kieran McCusker

Discussion: https://postgr.es/m/CAGgUQ6H6qYScctOhktQ9HLFDDoafBKHyUgJbZ6q_dOApnzNTXg@mail.gmail.com
This commit is contained in:
Tom Lane
2023-05-02 17:55:01 -04:00
parent 08237056f8
commit 6489875ce6
3 changed files with 32 additions and 10 deletions
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13
doc/src/sgml/plpython.sgml
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@@ -789,7 +789,7 @@ $$ LANGUAGE plpython3u;
<variablelist>
<varlistentry>
<term><literal>plpy.<function>execute</function>(<replaceable>query</replaceable> [, <replaceable>max-rows</replaceable>])</literal></term>
<term><literal>plpy.<function>execute</function>(<replaceable>query</replaceable> [, <replaceable>limit</replaceable>])</literal></term>
<listitem>
<para>
Calling <function>plpy.execute</function> with a query string and an
@@ -797,6 +797,15 @@ $$ LANGUAGE plpython3u;
be returned in a result object.
</para>
<para>
If <replaceable>limit</replaceable> is specified and is greater than
zero, then <function>plpy.execute</function> retrieves at
most <replaceable>limit</replaceable> rows, much as if the query
included a <literal>LIMIT</literal>
clause. Omitting <replaceable>limit</replaceable> or specifying it as
zero results in no row limit.
</para>
<para>
The result object emulates a list or dictionary object. The result
object can be accessed by row number and column name. For example:
@@ -887,7 +896,7 @@ foo = rv[i]["my_column"]
<varlistentry>
<term><literal>plpy.<function>prepare</function>(<replaceable>query</replaceable> [, <replaceable>argtypes</replaceable>])</literal></term>
<term><literal>plpy.<function>execute</function>(<replaceable>plan</replaceable> [, <replaceable>arguments</replaceable> [, <replaceable>max-rows</replaceable>]])</literal></term>
<term><literal>plpy.<function>execute</function>(<replaceable>plan</replaceable> [, <replaceable>arguments</replaceable> [, <replaceable>limit</replaceable>]])</literal></term>
<listitem>
<para>
<indexterm><primary>preparing a query</primary><secondary>in PL/Python</secondary></indexterm>