"please select equal number of source and reference" on sqlyog

I am trying to add a foreign key constraint via sqlyog, and getting this开发者_C百科 error, although I am only select one source and one reference columns

please select equal number of source and reference

Does anyone knows what it means in this case? Note that I do have an equal number of source and reference columns...

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I came across the same issue with SQLYog v9.01. The error message is misleading and the real cause of an error can be totally different.

Things I checked to solve this are the following:

• Check table engyne types, should be both InnoDb
• Check if your target table is not the same as source.
• Check datatypes, length and charset collation of referenced fields.
• If you already have data in your tables check its consistency.

For example, you should remove all unrelated data from table B which relates to table A

 DELETE target FROM B AS target LEFT JOIN A USING(id_A) WHERE A.id_A IS NULL

• Finally ones in my case I had to FLUSH tables to create my constraints successfully.

Manual constraint creation from Query window can give you more information on your error type.

Just a reminder:

ALTER TABLE `B` ADD CONSTRAINT `FK_B` FOREIGN KEY (`id_A`) REFERENCES `A` (`id_A`) ON DELETE CASCADE ; 

Good luck!