Oracle SQL, conditional foreign key - sql

Question

I have a problem with implementing DB. I have 2 tables:
CREATE TABLE TAB1
(
TAB1_ID INT NOT NULL PRIMARY KEY,
TAB1_BOOL VARCHAR(4) NOT NULL CHECK (TAB1_BOOL IN('OPT1', 'OPT2'))
);
CREATE TABLE TAB2
(
TAB2_ID INT NOT NULL
);
I would like to make TAB2_ID as foreign key of TAB1_ID, but TAB2_ID can be only these TAB1_IDs which rows in table TAB1 are marked with TAB1_BOOL == OPT1. For example:
TAB1 contains 2 rows:
1. 'TAB1_ID==1' 'TAB1_BOOL==OPT1',
2. 'TAB1_ID==2' 'TAB1_BOOL==OPT2'.
Now, statement like:
INSERT INTO TAB2 (TAB2_ID) VALUES (2);
should be rejected because row with TAB1_ID==2 is marked with OPT2
Is it possible to make this in Oracle SQL ?

Answer 1

This can be achieved by using a trigger:
CREATE TABLE TAB1 (
TAB1_ID INT NOT NULL PRIMARY KEY,
TAB1_BOOL VARCHAR(4) NOT NULL CHECK (TAB1_BOOL IN('OPT1', 'OPT2'))
);
CREATE TABLE TAB2 (
TAB2_ID INT NOT NULL,
FOREIGN KEY (TAB2_ID) REFERENCES TAB1 (TAB1_ID)
);
CREATE OR REPLACE TRIGGER CHECK_TAB2_ID
BEFORE UPDATE OR INSERT ON TAB2 FOR EACH ROW
DECLARE
CURSOR CHECK_CURSOR IS
SELECT TAB1_BOOL
FROM TAB1
WHERE TAB1_ID = :new.TAB2_id;
V_TAB1_BOOL VARCHAR(4);
BEGIN
OPEN CHECK_CURSOR;
FETCH CHECK_CURSOR INTO V_TAB1_BOOL;
IF (V_TAB1_BOOL <> 'OPT1') THEN
CLOSE CHECK_CURSOR;
raise_application_error(10000, 'Wrong value in TAB1');
END IF;
CLOSE CHECK_CURSOR;
END;
INSERT INTO TAB1 VALUES (1, 'OPT1');
INSERT INTO TAB1 VALUES (2, 'OPT2');
INSERT INTO TAB2 (TAB2_ID) VALUES (1);
There is still a small error in the trigger above. I have currently no access to an Oracle database, so I can hardy fix it. Here's my Fiddle.
p.s.: ok, just a ; missing in the Fiddle - here's an update.