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CREATE TABLE test (`day` ENUM('Sun','Mon','Tue','Wed','Fri','Sat'), `time` CHAR(8));
CREATE UNIQUE INDEX idx
ON test ((CASE WHEN `day`='Sun' AND `time`='09:00 am' THEN 0 ELSE NULL END));
Records: 0 Duplicates: 0 Warnings: 0
INSERT INTO test VALUES
('Sun', '09:00 am'),
('Sun', '10:00 am'),
('Mon', '09:00 am'),
('Mon', '10:00 am'),
('Mon', '09:00 am'); -- allowed duplicate
SELECT * FROM test;
Records: 5 Duplicates: 0 Warnings: 0
| day | time |
|---|---|
| Sun | 09:00 am |
| Sun | 10:00 am |
| Mon | 09:00 am |
| Mon | 10:00 am |
| Mon | 09:00 am |
INSERT INTO test VALUES
('Sun', '09:00 am'); -- non-allowed duplicate
Duplicate entry '0' for key 'test.idx'