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Commit6489875

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Doc: clarify behavior of row-limit arguments in the PLs' SPI wrappers.
plperl, plpython, and pltcl all provide query-execution functionsthat 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". Howeverthe PLs' documentation failed to explain this special behavior ofzero, so that a reader might well assume it means "fetch zerorows". Improve that.Daniel Gustafsson and Tom Lane, per report from Kieran McCuskerDiscussion:https://postgr.es/m/CAGgUQ6H6qYScctOhktQ9HLFDDoafBKHyUgJbZ6q_dOApnzNTXg@mail.gmail.com
1 parent0823705 commit6489875

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‎doc/src/sgml/plperl.sgml

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@@ -441,17 +441,25 @@ use strict;
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<variablelist>
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<varlistentry>
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<term>
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<literal><function>spi_exec_query</function>(<replaceable>query</replaceable> [, <replaceable>max-rows</replaceable>])</literal>
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<literal><function>spi_exec_query</function>(<replaceable>query</replaceable> [, <replaceable>limit</replaceable>])</literal>
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<indexterm>
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<primary>spi_exec_query</primary>
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<secondary>in PL/Perl</secondary>
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</indexterm>
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</term>
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<listitem>
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<para>
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<literal>spi_exec_query</literal> executes an SQL command and
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returns the entire row set as a reference to an array of hash
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references. <emphasis>You should only use this command when you know
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<function>spi_exec_query</function> executes an SQL command and
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returns the entire row set as a reference to an array of hash references.
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If <replaceable>limit</replaceable> is specified and is greater than zero,
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then <function>spi_exec_query</function> retrieves at
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most <replaceable>limit</replaceable> rows, much as if the query included
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a <literal>LIMIT</literal> clause. Omitting <replaceable>limit</replaceable>
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or specifying it as zero results in no row limit.
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</para>
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<para>
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<emphasis>You should only use this command when you know
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that the result set will be relatively small.</emphasis> Here is an
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example of a query (<command>SELECT</command> command) with the
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optional maximum number of rows:
@@ -643,7 +651,10 @@ $plan = spi_prepare('SELECT * FROM test WHERE id &gt; $1 AND name = $2',
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by <literal>spi_exec_query</literal>, or in <literal>spi_query_prepared</literal> which returns a cursor
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exactly as <literal>spi_query</literal> does, which can be later passed to <literal>spi_fetchrow</literal>.
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The optional second parameter to <literal>spi_exec_prepared</literal> is a hash reference of attributes;
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the only attribute currently supported is <literal>limit</literal>, which sets the maximum number of rows returned by a query.
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the only attribute currently supported is <literal>limit</literal>, which
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sets the maximum number of rows returned from the query.
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Omitting <literal>limit</literal> or specifying it as zero results in no
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row limit.
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</para>
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<para>

‎doc/src/sgml/plpython.sgml

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@@ -789,14 +789,23 @@ $$ LANGUAGE plpython3u;
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<variablelist>
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<varlistentry>
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<term><literal>plpy.<function>execute</function>(<replaceable>query</replaceable> [, <replaceable>max-rows</replaceable>])</literal></term>
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<term><literal>plpy.<function>execute</function>(<replaceable>query</replaceable> [, <replaceable>limit</replaceable>])</literal></term>
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<listitem>
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<para>
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Calling <function>plpy.execute</function> with a query string and an
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optional row limit argument causes that query to be run and the result to
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be returned in a result object.
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</para>
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<para>
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If <replaceable>limit</replaceable> is specified and is greater than
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zero, then <function>plpy.execute</function> retrieves at
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most <replaceable>limit</replaceable> rows, much as if the query
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included a <literal>LIMIT</literal>
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clause. Omitting <replaceable>limit</replaceable> or specifying it as
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zero results in no row limit.
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</para>
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<para>
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The result object emulates a list or dictionary object. The result
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object can be accessed by row number and column name. For example:
@@ -887,7 +896,7 @@ foo = rv[i]["my_column"]
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<varlistentry>
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<term><literal>plpy.<function>prepare</function>(<replaceable>query</replaceable> [, <replaceable>argtypes</replaceable>])</literal></term>
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<term><literal>plpy.<function>execute</function>(<replaceable>plan</replaceable> [, <replaceable>arguments</replaceable> [, <replaceable>max-rows</replaceable>]])</literal></term>
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<term><literal>plpy.<function>execute</function>(<replaceable>plan</replaceable> [, <replaceable>arguments</replaceable> [, <replaceable>limit</replaceable>]])</literal></term>
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<listitem>
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<para>
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<indexterm><primary>preparing a query</primary><secondary>in PL/Python</secondary></indexterm>

‎doc/src/sgml/pltcl.sgml

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Original file line numberDiff line numberDiff line change
@@ -341,9 +341,11 @@ $$ LANGUAGE pltcl;
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</para>
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<para>
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The optional <literal>-count</literal> value tells
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<function>spi_exec</function> the maximum number of rows
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to process in the command. The effect of this is comparable to
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setting up a query as a cursor and then saying <literal>FETCH <replaceable>n</replaceable></literal>.
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<function>spi_exec</function> to stop
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once <replaceable>n</replaceable> rows have been retrieved,
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much as if the query included a <literal>LIMIT</literal> clause.
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If <replaceable>n</replaceable> is zero, the query is run to
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completion, the same as when <literal>-count</literal> is omitted.
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</para>
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<para>
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If the command is a <command>SELECT</command> statement, the values of the

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