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Marginal improvements to documentation of plpgsql's OPEN cursor statement.

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Rearrange text to improve clarity, and add an example of implicit reference
to a plpgsql variable in a bound cursor's query.  Byproduct of some work
I'd done on the "named cursor parameters" patch before giving up on it.
This commit is contained in:
Tom Lane 2011-10-15 13:02:37 -04:00
parent b4aec388d8
commit 0898d71f66
1 changed files with 28 additions and 16 deletions
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44
doc/src/sgml/plpgsql.sgml
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@ -2720,7 +2720,7 @@ END;
DECLARE
curs1 refcursor;
curs2 CURSOR FOR SELECT * FROM tenk1;
curs3 CURSOR (key integer) IS SELECT * FROM tenk1 WHERE unique1 = key;
curs3 CURSOR (key integer) FOR SELECT * FROM tenk1 WHERE unique1 = key;
</programlisting>
All three of these variables have the data type <type>refcursor</>,
but the first can be used with any query, while the second has
@ -2836,31 +2836,43 @@ OPEN <replaceable>bound_cursorvar</replaceable> <optional> ( <replaceable>argume
cursor cannot be open already. A list of actual argument value
expressions must appear if and only if the cursor was declared to
take arguments. These values will be substituted in the query.
</para>
<para>
The query plan for a bound cursor is always considered cacheable;
there is no equivalent of <command>EXECUTE</command> in this case.
Notice that <literal>SCROLL</> and
<literal>NO SCROLL</> cannot be specified, as the cursor's scrolling
Notice that <literal>SCROLL</> and <literal>NO SCROLL</> cannot be
specified in <command>OPEN</>, as the cursor's scrolling
behavior was already determined.
</para>
<para>
Note that because variable substitution is done on the bound
cursor's query, there are two ways to pass values into the cursor:
either with an explicit argument to <command>OPEN</>, or
implicitly by referencing a <application>PL/pgSQL</> variable
in the query. However, only variables declared before the bound
cursor was declared will be substituted into it. In either case
the value to be passed is determined at the time of the
<command>OPEN</>.
</para>
<para>
Examples:
Examples (these use the cursor declaration examples above):
<programlisting>
OPEN curs2;
OPEN curs3(42);
</programlisting>
</para>
</para>
<para>
Because variable substitution is done on a bound cursor's query,
there are really two ways to pass values into the cursor: either
with an explicit argument to <command>OPEN</>, or implicitly by
referencing a <application>PL/pgSQL</> variable in the query.
However, only variables declared before the bound cursor was
declared will be substituted into it. In either case the value to
be passed is determined at the time of the <command>OPEN</>.
For example, another way to get the same effect as the
<literal>curs3</> example above is
<programlisting>
DECLARE
key integer;
curs4 CURSOR FOR SELECT * FROM tenk1 WHERE unique1 = key;
BEGIN
key := 42;
OPEN curs4;
</programlisting>
</para>
</sect3>
</sect2>