Syntax error in my trigger in POSTGRESQL

Question

I need to create triggers for an exercice, i have 3 tables, which one have one int argument and i want to create this trigger:

   CREATE TRIGGER D1_1 BEFORE INSERT ON T1 FOR EACH ROW 
   WHEN((SELECT COUNT(*) FROM T2) < 1)
   INSERT INTO T2 VALUES(6) 
   END;

Syntaxe error near THEN..

Thank you!

This is not how a trigger is created in Postgres. Please see the examples in the manual: postgresql.org/docs/current/static/plpgsql-trigger.html — user330315
– user330315, Commented Jan 15, 2017 at 13:49

Gordon Linoff · Accepted Answer · 2017-01-15 13:07:12Z

1

You don't even need conditional logic:

    INSERT INTO T2
        SELECT 6
        WHERE NOT EXISTS (SELECT 1 FROM t2);

Note that NOT EXISTS is generally more efficient than COUNT(*) = 0. NOT EXISTS stops at the first matching row, rather going through the entire table to count everything -- and then doing something if there are no rows.

answered Jan 15, 2017 at 13:07

Gordon Linoff

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2 Comments

valt Over a year ago

No, i really need this trigger, cuz i have 5 others triggers and they are linked, i need this trigger ^^

Gordon Linoff Over a year ago

@valt . . . You can incorporate this logic into a trigger. I left out the trigger definition, because it would seem to distract from the logic of the query.

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