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>35.2. Visibility of Data Changes</A
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> If you execute SQL commands in your trigger function, and these
commands access the table that the trigger is for, then
you need to be aware of the data visibility rules, because they determine
whether these SQL commands will see the data change that the trigger
is fired for. Briefly:
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> The data change (insertion, update, or deletion) causing the trigger
to fire is naturally
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> visible to SQL commands executed in a
before trigger, because it hasn't happened yet.
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> However, SQL commands executed in a before trigger
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> see the effects of data changes
for rows previously processed in the same outer command. This
requires caution, since the ordering of these change events
is not in general predictable; a SQL command that affects
multiple rows may visit the rows in any order.
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> When an after trigger is fired, all data changes made by the outer
command are already complete, and are visible to executed SQL commands.
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> Further information about data visibility rules can be found in
<A
HREF="spi-visibility.html"
>Section 41.4</A
>. The example in <A
HREF="trigger-example.html"
>Section 35.4</A
> contains a demonstration of these rules.
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