Question

I have just discovered my database which has been moved between a few servers in the last few months was, in one of the database dumps, converted to myisam and all the foreign key constraints nuked (not impressed). I’ve converted all the tables back to innodb with a php script but now I’m finding half the constraints are failing to add.

Error Code: 1452. Cannot add or update a child row: a foreign key constraint fails (`identicar2`.<result 2 when explaining filename '#sql-2a7_c0'>, CONSTRAINT `#sql-2a7_c0_ibfk_1` FOREIGN KEY (`feature_sk`) REFERENCES `tbl_feature_list` (`feature_sk`))

I’m lost now, I can’t go through thousands of records manually. what is the best thing to do in order to get my database back into shape?

I can provide table structures if you want but I imagine any solution will be independant of the exact structure anyway

Answer 1

The simplest solution: (containing the obvious danger of losing data you may want to keep)

UPDATE table
SET fkColumn = NULL
WHERE fkColumn NOT IN (SELECT referenceColumn FROM referencedTable)

If you just want to find them:

SELECT *
FROM table
WHERE fkColumn NOT IN (SELECT referenceColumn FROM referencedTable)