CREATE TABLE `FOLLOWERS` (`FOLLOWER_ID` char(255) COLLATE utf8_unicode_ci NOT NULL, `FOLLOWING_ID` char(255) COLLATE utf8_unicode_ci NOT NULL, `FOLLOWING_IN` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci
How to prevent repeated input in multiple columns?
For example, I don’t need something like this
| FOLLOWER_ID | FOLLOWING_ID | FOLLOWING_IN |
|---|---|---|
| 283 | 283 | ... |
| 193 | 283 | ... |
| 908 | 908 | ... |
I want to ask, does the followers table look well designed?
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If you are using MySQL 8.0.16 or later, you can use
CHECKconstraints.CREATE TABLE `FOLLOWERS` ( `FOLLOWER_ID` char(255) COLLATE utf8_unicode_ci NOT NULL, `FOLLOWING_ID` char(255) COLLATE utf8_unicode_ci NOT NULL, `FOLLOWING_IN` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP, CONSTRAINT CHECK (FOLLOWER_ID != FOLLOWING_ID) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ciIf you are using an older version, see Can MySQL triggers emulate CHECK constraints? Learn how to use triggers to simulate check constraints.