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<chapter id="triggers">

</para>

<para>

A trigger function must return either <symbol>NULL</> or a

<structname>HeapTuple</> pointer. Be careful to return either

A trigger function must return either a

<structname>HeapTuple</> pointer or a <symbol>NULL</> pointer

(<emphasis>not</> a SQL NULL, that is, do not set isNull true).

Be careful to return either

<structfield>tg_trigtuple</> or <structfield>tg_newtuple</>,

as appropriate, if you don't want to modify the row being operated on.

</para>