MySQL drop field; foreign key errorno 150

Question

Problems with MySQL using InnoDB and dropping an unused, foreign key. The foreign key references another table's id. However, I don't need this field.

I've tried removing the fk index, which doesn't work - says it's needed in a foreign key contraint. And removing the field, which gives me an error:

1025 - Error on rename of './axis/#sql-ad8_1531' to './axis/Schedule' (errno: 150)

The table is currently empty. There are no tables referencing this field. Any ideas on how to get rid of this? Other than creating a new table?

If I'm reading the below error correctly, I can't drop the column since the fk index is declared. And I can't drop the index, because the column exists. Chicken & Egg??

LATEST FOREIGN KEY ERROR 111004 17:05:40 Error in foreign key constraint of table axis/Schedule: there is no index in the table which would contain the columns as the first columns, or the data types in the table do not match the ones in the referenced table or one of the ON ... SET NULL columns is declared NOT NULL. Constraint: , CONSTRAINT "fk_Schedule_Grp" FOREIGN KEY ("idGrp") REFERENCES "Grp" ("idGrp") ON DELETE NO ACTION ON UPDATE NO ACTION InnoDB: Renaming table axis. to axis.Schedule failed!

Answer 1

You need to use

ALTER TABLE table_name DROP FOREIGN KEY constraint_name

Here constraint_name is the name of the constraint rather than the index. If you do not know what this is, you can find out by issuing a SHOW CREATE TABLE. It is the identifier that appears after the word CONSTRAINT.

Edit: From your addition to the question, it looks like you need to issue

ALTER TABLE table_name DROP FOREIGN KEY fk_Schedule_Grp