Drop constraint by stored in a variable name with special characters in Postgresql

Question

I want to drop constraint with the name unknown so I use the following code:

EXECUTE 'ALTER TABLE public."IntravenousTherapyAppointment" DROP CONSTRAINT '||fk_Name||';';

The problem is that fk_Name ends with '~' so I get syntax error.

The full code:

DO $$
DECLARE fk_Name TEXT;
BEGIN
    fk_Name := (SELECT
                tc.constraint_name
                FROM
                information_schema.table_constraints AS tc
                JOIN information_schema.key_column_usage AS kcu
                ON tc.constraint_name = kcu.constraint_name
                AND tc.table_schema = kcu.table_schema
                JOIN information_schema.constraint_column_usage AS ccu
                ON ccu.constraint_name = tc.constraint_name
                AND ccu.table_schema = tc.table_schema
                WHERE constraint_type = 'FOREIGN KEY' AND tc.table_name='IntravenousTherapyAppointment' AND ccu.table_name='MedicamentMeasurementUnit');
    IF fk_Name IS NOT NULL THEN
        EXECUTE 'ALTER TABLE public."IntravenousTherapyAppointment" DROP CONSTRAINT '||fk_Name||';';
    END IF;
END $$;

SABER · Accepted Answer · 2018-10-22 09:12:12Z

1

this should fix your problem:

DO $$
DECLARE fk_Name TEXT;
BEGIN
    fk_Name := (SELECT
                tc.constraint_name
                FROM
                information_schema.table_constraints AS tc
                JOIN information_schema.key_column_usage AS kcu
                ON tc.constraint_name = kcu.constraint_name
                AND tc.table_schema = kcu.table_schema
                JOIN information_schema.constraint_column_usage AS ccu
                ON ccu.constraint_name = tc.constraint_name
                AND ccu.table_schema = tc.table_schema
                WHERE constraint_type = 'FOREIGN KEY' AND tc.table_name='IntravenousTherapyAppointment' AND ccu.table_name='MedicamentMeasurementUnit');
    IF fk_Name IS NOT NULL THEN
        EXECUTE 'ALTER TABLE public."IntravenousTherapyAppointment" DROP CONSTRAINT "'||fk_Name||'";';
    END IF;
END $$;

P.S: Be careful while handling the objects/constraints having double quoted names.

answered Oct 22, 2018 at 9:12

SABER

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1 Comment

99Sono Over a year ago

I had problems with that type of varible assignment in my posgres DB. I needed to it similar to oracle with: SELECT constraint_name INTO fk_Name. Also a good idea in PL scripts is to use the RAISE NOTICE 'SOME text to be logged out'; to see where the script is navigating into.

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