Create a trigger in postgresql

Question

I have a problem with my trigger:

CREATE OR REPLACE FUNCTION process_fillDerivedFrom_used() RETURNS TRIGGER AS $fillDerivedFrom_used$
  DECLARE
    prog      varchar(255);
    current   varchar(255);
  BEGIN
    SELECT u.iduseentity as prog ,g.idCreatedEntity as current
    FROM entity e
    JOIN used u ON e.identity=u.iduseentity
    JOIN activity a ON a.idactivity=u.idusedactivity
    JOIN generatedby g ON g.idcreatoractivity=a.idactivity

    INSERT INTO DERIVEDFROM VALUES (prog,current)
  END;

$fillDerivedFrom_used$ LANGUAGE plpgsql;
CREATE TRIGGER fillDerivedFrom_used
AFTER INSERT OR UPDATE OR DELETE ON emp
    FOR EACH ROW EXECUTE PROCEDURE process_fillDerivedFrom_used();

I use 3 tables, the query is correct so I think the error doesn't come from here. But when I copy past this trigger in my terminal nothing happen, no error message, I can write in terminal but I can't execute any query, like I have forgot something in my trigger so I think it's not completely created I think.

I think I mix 2 languages PL/SQL that I have learn at school and the postgresql.

Thank you for you help

you should select into variable, not as alias... and you miss semicolon after select — Vao Tsun
– Vao Tsun, Commented Apr 25, 2017 at 9:47
and a definition of you function looks strange - you want to query that four table join on each row of emp?.. and why not insert into DERIVEDFROM select ...all_your_select...?.. keep in mind - you dont operate NEW or OLD record here - it does not look like trigger function at all — Vao Tsun
– Vao Tsun, Commented Apr 25, 2017 at 9:50

Gordon Linoff · Accepted Answer · 2017-04-25 12:22:48Z

I don't know what problems you are having. One is obvious. as is not used for variables; into is. Also, you should name variables so they do not conflict with column names:

CREATE OR REPLACE FUNCTION process_fillDerivedFrom_used() RETURNS TRIGGER AS $fillDerivedFrom_used$
  DECLARE
    prog      v_varchar(255);
    current   v_varchar(255);
  BEGIN
    SELECT u.iduseentity as prog, g.idCreatedEntity as current
    INTO v_proc, v_current
    FROM entity e JOIN
         used u
         ON e.identity = u.iduseentity JOIN
         activity a
         ON a.idactivity = u.idusedactivity JOIN
         generatedby g
         ON g.idcreatoractivity = a.idactivity

    INSERT INTO DERIVEDFROM VALUES (v_prog, v_current)
END;

Of course, this begs the question of why you are using variables at all:

CREATE OR REPLACE FUNCTION process_fillDerivedFrom_used() RETURNS TRIGGER AS $fillDerivedFrom_used$
  BEGIN
    INSERT INTO DERIVEDFROM (prog, current)  -- or whatever the column names are
        SELECT u.iduseentity as prog, g.idCreatedEntity as current
        FROM entity e JOIN
             used u
             ON e.identity = u.iduseentity JOIN
             activity a
             ON a.idactivity = u.idusedactivity JOIN
             generatedby g
             ON g.idcreatoractivity = a.idactivity;    
END;

Fedour · Accepted Answer · 2017-04-25 12:00:50Z

I've done that and it's work, thank you for your help!

CREATE OR REPLACE FUNCTION process_fillDerivedFromGenby() RETURNS TRIGGER AS $fillDerivedFromgenby$
  DECLARE
    prog     varchar(255);
    curent   varchar(255);
  BEGIN

    SELECT u.iduseentity , g.idCreatedEntity into prog,curent
    FROM entity e
    JOIN used u ON e.identity=u.iduseentity
    JOIN activity a ON a.idactivity=u.idusedactivity
    JOIN generatedby g ON g.idcreatoractivity=a.idactivity
    WHERE g.idCreatedEntity =NEW.idCreatedEntity;

    --raise notice 'curent: "%" prog by "%"', curent, prog;

    INSERT INTO DERIVEDFROM VALUES(prog,curent);
    return new;
  END;

$fillDerivedFromgenby$ LANGUAGE plpgsql;
CREATE TRIGGER fillDerivedFromgenby AFTER INSERT ON GENERATEDBY
    FOR EACH ROW EXECUTE PROCEDURE process_fillDerivedFromGenby();

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