Solutions to IT problems

Solutions I found when learning new IT stuff

MySQL varchar foreign key

with one comment

How to waste hours for a simple Issue

I wanted to add a varchar(8) foreign key to a table but MySQL consistently complained with errno 150. I really almost lost my mind as why this would not work. Also


did not reveal anything too meaningful:

FOREIGN KEY (`userId`) REFERENCES `user` (`userId`):
Cannot find an index in the referenced table where the
referenced columns appear as the first columns, or column types
in the table and the referenced table do not match for constraint.
Note that the internal storage type of ENUM and SET changed in
tables created with >= InnoDB-4.1.12, and such columns in old tables
cannot be referenced by such columns in new tables.
for correct foreign key definition.


The thing that caught my attention was

column types in the table and the referenced table do not match for constraint


I thought why would 2 varchar columns with same size not match in type? And of course the answer is obvious collation. Turns out the that in the new table the column was UTF-8 instead of ASCII as in the referenced table. Changed to ascii and done.

Never had such issues before but I’m more used to Oracle and AFAIK there is now “column level collation” in Oracle.


Written by kienerj

November 14, 2011 at 14:00

Posted in Database, MySQL

One Response

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  1. Thanks for the post and solution. I don’t think I would have ever found that…

    February 7, 2012 at 05:16

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