MySQL 8.0 | db<>fiddle


	CREATE TABLE tableA (id VARCHAR(255)); CREATE TABLE tableB (id VARCHAR(255)); CREATE TABLE tableC (id VARCHAR(255)); ✓ ✓ ✓
	hidden batch(es)


	CREATE TABLE tableABC (id VARCHAR(255) UNIQUE); CREATE TRIGGER tr_bi_a BEFORE INSERT ON tableA FOR EACH ROW INSERT INTO tableABC VALUES (NEW.id); CREATE TRIGGER tr_bi_b BEFORE INSERT ON tableB FOR EACH ROW INSERT INTO tableABC VALUES (NEW.id); CREATE TRIGGER tr_bi_c BEFORE INSERT ON tableC FOR EACH ROW INSERT INTO tableABC VALUES (NEW.id); ✓ ✓ ✓ ✓
	hidden batch(es)


	INSERT INTO tableA VALUES ('keyA'); -- success INSERT INTO tableB VALUES ('keyB'); -- success INSERT INTO tableC VALUES ('keyC'); -- success INSERT INTO tableA VALUES ('keyAA'); -- success INSERT INTO tableB VALUES ('keyBB'); -- success ✓ ✓ ✓ ✓ ✓ ✓
	hidden batch(es)


	INSERT INTO tableC VALUES ('keyC'); -- already present in tableC Duplicate entry 'keyC' for key 'tableABC.id'
	hidden batch(es)


	INSERT INTO tableA VALUES ('keyC'); -- already present in tableC Duplicate entry 'keyC' for key 'tableABC.id'
	hidden batch(es)


	INSERT INTO tableB VALUES ('keyA'); -- already present in tableA Duplicate entry 'keyA' for key 'tableABC.id'
	hidden batch(es)


	INSERT INTO tableC VALUES ('keyABC'); -- success ✓ ✓
	hidden batch(es)