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POPostgreSQL triggers and exceptions
 

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    <p>I'm trying to get my first ever trigger and function to work, but how I throw exceptions and return data right way?</p> <p>PostgreSQL 8.4.1</p> <pre><code>CREATE TABLE "SHIFTS" ( id integer NOT NULL, -- SERIAL added timestamp without time zone DEFAULT now() NOT NULL, starts timestamp without time zone NOT NULL, ends timestamp without time zone NOT NULL, employee_id integer, modified timestamp without time zone, status integer DEFAULT 1 NOT NULL, billid integer, CONSTRAINT "SHIFTS_check" CHECK ((starts &lt; ends)) ); -- Check if given shift time overlaps with existing data CREATE OR REPLACE FUNCTION shift_overlaps (integer, timestamp, timestamp) RETURNS boolean AS $$ DECLARE _employeeid ALIAS FOR $1; _start ALIAS FOR $2; _end ALIAS FOR $3; BEGIN SELECT COUNT(id) AS c FROM "SHIFTS" WHERE employee_id = _employeeid AND status = 1 AND ( (starts BETWEEN _start AND _end) OR (ends BETWEEN _start AND _end) ) ; -- Return boolean RETURN (c &gt; 0); END; $$ LANGUAGE plpgsql ; CREATE OR REPLACE FUNCTION check_shift() RETURNS trigger AS ' BEGIN -- Bill ID is set, do not allow update IF tg_op = "UPDATE" THEN IF old.billid IS NOT NULL THEN RAISE EXCEPTION "Shift is locked" END IF; END IF; -- Check for overlap IF tg_op = "INSERT" THEN IF new.employee_id IS NOT NULL THEN IF shift_overlaps(new.employee_id, new.starts, new.ends) THEN RAISE EXCEPTION "Given time overlaps with shifts" END IF; END IF; END IF; -- Check for overlap IF tg_op = "UPDATE" THEN IF (new.employee_id IS NOT NULL) AND (new.status = 1) THEN IF shift_overlaps(new.employee_id, new.starts, new.ends) THEN RAISE EXCEPTION "Given time overlaps with shifts" END IF; END IF; END IF; RETURN new; END ' LANGUAGE plpgsql ; -- Shift checker trigger CREATE TRIGGER check_shifts BEFORE INSERT OR UPDATE ON "SHIFTS" FOR EACH ROW EXECUTE PROCEDURE check_shift() ; </code></pre> <p>shift_overlaps():</p> <pre><code>SQL error: ERROR: query has no destination for result data </code></pre> <p>check_shift():</p> <pre><code>SQL error: ERROR: unrecognized exception condition "Shift is locked" </code></pre>
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