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Asked: 2026-05-26T23:14:30+00:00

I have a question regarding Foreign Keys in an InnoDB Table. I have 4

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I have a question regarding Foreign Keys in an InnoDB Table. I have 4 tables in my database:

Signup:

  • UID – Primary Key
  • Afid
  • Planid
  • Industryid

Affiliates:

  • Afid – Primary Key

Plans:

  • Planid – Primary Key

Industries:

  • Industryid – Primary Key

SQL I use to add the keys:

CONSTRAINT `FK_signup_industries` FOREIGN KEY (`industryid`) REFERENCES `industries` (`industryid`) ON UPDATE CASCADE ON DELETE CASCADE,
CONSTRAINT `FK_signup_affiliates` FOREIGN KEY (`afid`) REFERENCES `affiliates` (`afid`) ON UPDATE CASCADE ON DELETE CASCADE,
CONSTRAINT `FK_signup_plans` FOREIGN KEY (`planid`) REFERENCES `plans` (`planid`) ON UPDATE CASCADE ON DELETE CASCADE

What my question is:

If I was to delete a plan or an industry on their respective tables would the user in the signup table be deleted? I have tried to find guides on this and they don’t explain it very well.

Basically what I need done is that the row in the signup table never to be deleted no matter what. When I use this query:

CONSTRAINT `FK_signup_plans` FOREIGN KEY (`planid`) REFERENCES `plans` (`planid`) ON UPDATE CASCADE ON DELETE NO ACTION

I get this error:

Cannot delete a parent row.
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1 Answer

  1. Editorial Team

    If you need the row in Signup to stay even if you delete the referenced row in Industries, Affiliates, or Plans, then you have two choices:

    • Do not declare a foreign key constraint. This removes enforcement of referential integrity, but it allows rows to exist in Signup that reference a parent primary key value that no longer exists.

    • Use ON DELETE SET NULL. This allows the row to stay, but the foreign key value that references the now-deleted parent will be changed.*

    For more details see http://dev.mysql.com/doc/refman/5.5/en/innodb-foreign-key-constraints.html

    * The standard SQL specification also defines a rule ON DELETE SET DEFAULT, but InnoDB doesn’t support this feature.

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