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mysql on update cascade not working


By : Chethan
Date : May 05 2020, 08:34 AM

If I have two tables the first I have table B with foreign key reference to table A (set to ON UPDATE CASCADE) and I run a

LOAD DATA INFILE file.txt REPLACE INTO TABLE A;

will the references update properly?

Please note that I'm not talking about ON DELETE CASCADE; I know a REPLACE command will delete records in table B if I have set that .

Answer :

MySQL does not fire the update event as result of a replace query, only the delete. Here's why:

REPLACE works exactly like INSERT, except that if an old row in the table has the same value as a new row for a PRIMARY KEY or a UNIQUE index, the old row is deleted before the new row is inserted.

(From the MySQL 5.0 Reference Manual)

I have foreign key set with ON UPDATE CASCADE ON DELETE SET NULL, and whenever I do a REPLACE to the foreign table's primary key, the foreign key in my related table gets set to NULL.



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