check constraint won't work mysql [duplicate]

Answer 1

MySQL doesn't enforce check constraints.

This is a well documented deviation from the SQL standard. (Though it unexpected by the uninitiated.)

If you need the MySQL database to enforce a "check constraint", the enforcement has to be coded into a BEFORE INSERT and a BEFORE UPDATE trigger.

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This note:

The CHECK clause is parsed but ignored by all storage engines.

is buried in the MySQL Reference Manual, under the CREATE TABLE syntax.

Reference: https://dev.mysql.com/doc/refman/5.5/en/create-table.html

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WARNING ABOUT ENUM

An ENUM does not restrict "invalid" values from being inserted; an invalid value is translated into a zero length string, a warning is issued, but it's not an error.

Demonstration:

CREATE TABLE foo (gen ENUM('M','F'))

INSERT INTO foo (gen) VALUES ('x')

-- Warning Code : 1265
-- Data truncated for column 'gen' at row 1

SELECT gen, CHAR_LENGTH(gen) FROM foo;

-- gen  CHAR_LENGTH(gen)  
-- ---  ----------------
--                     0