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Add support for \aset in pgbench

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This option is similar to \gset, except that it is able to store all
results from combined SQL queries into separate variables.  If a query
returns multiple rows, the last result is stored and if a query returns
no rows, nothing is stored.

While on it, add a TAP test for \gset to check for a failure when a
query returns multiple rows.

Author: Fabien Coelho
Reviewed-by: Ibrar Ahmed, Michael Paquier
Discussion: https://postgr.es/m/alpine.DEB.2.21.1904081914200.2529@lancre
This commit is contained in:
Michael Paquier
2020-04-03 11:45:15 +09:00
parent ed7a509571
commit 9d8ef98800
3 changed files with 104 additions and 19 deletions
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22
doc/src/sgml/ref/pgbench.sgml
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@ -1057,18 +1057,29 @@ pgbench <optional> <replaceable>options</replaceable> </optional> <replaceable>d
<varlistentry id='pgbench-metacommand-gset'>
<term>
<literal>\gset [<replaceable>prefix</replaceable>]</literal>
<literal>\aset [<replaceable>prefix</replaceable>]</literal>
</term>
<listitem>
<para>
This command may be used to end SQL queries, taking the place of the
These commands may be used to end SQL queries, taking the place of the
terminating semicolon (<literal>;</literal>).
</para>
<para>
When this command is used, the preceding SQL query is expected to
return one row, the columns of which are stored into variables named after
column names, and prefixed with <replaceable>prefix</replaceable> if provided.
When the <literal>\gset</literal> command is used, the preceding SQL query is
expected to return one row, the columns of which are stored into variables
named after column names, and prefixed with <replaceable>prefix</replaceable>
if provided.
</para>
<para>
When the <literal>\aset</literal> command is used, all combined SQL queries
(separated by <literal>\;</literal>) have their columns stored into variables
named after column names, and prefixed with <replaceable>prefix</replaceable>
if provided. If a query returns no row, no assignment is made and the variable
can be tested for existence to detect this. If a query returns more than one
row, the last value is kept.
</para>
<para>
@ -1077,6 +1088,8 @@ pgbench <optional> <replaceable>options</replaceable> </optional> <replaceable>d
<replaceable>p_two</replaceable> and <replaceable>p_three</replaceable>
with integers from the third query.
The result of the second query is discarded.
The result of the two last combined queries are stored in variables
<replaceable>four</replaceable> and <replaceable>five</replaceable>.
<programlisting>
UPDATE pgbench_accounts
SET abalance = abalance + :delta
@ -1085,6 +1098,7 @@ UPDATE pgbench_accounts
-- compound of two queries
SELECT 1 \;
SELECT 2 AS two, 3 AS three \gset p_
SELECT 4 AS four \; SELECT 5 AS five \aset
</programlisting>
</para>
</listitem>