How to validate data in sql server?

Question

I have an issue related to data in sql server. In my database some of the constraint were not enabled ie they were not checked , After some time working on it we found this issue that a parent rows can be deleted without deleting child, which was an issue. I enabled all the constraint in the database using query

ALTER TABLE tbl_name CHECK CONSTRAINT ALL 

above query was executed on all the tables of that database without any error . But my concern is whether it will work or not , if it will work on the existing data then what will happen to that data whose parent table data has been deleted.

I want to know is there any way such that I can validate such data data whose parent record doesn't exist in the entire database. There are about 270 constraint containing FOREIGN KEY AND UNIQUE KEY . I don't want to go for manual option.

Please help me out.

Answer 1

ALTER TABLE tbl_name CHECK CONSTRAINT ALL

only re-enables the constraints. Importantly, the constraints are not checked against the existing data in the database (nor are they trusted by the optimizer). If you want that to occur, you need to specify WITH CHECK as well:

ALTER TABLE tbl_name WITH CHECK CHECK CONSTRAINT ALL

(And yes, the word CHECK appears twice)

If you execute this, and there are orphaned child rows (or other invalid constraints), then the ALTER TABLE will fail with an error message. There's nothing SQL Server can do to fix this issue - it's for you to decide whether to a) remove the orphaned rows, or b) to re-create, in some manner, a suitable parent row for them.

Answer 2

You can also add the 'ON DELETE CASCADE' code to the end of foreign keys to prevent orphaned child rows from persisting.

This is more of a 'better practice' going forward than a solution, but I believe Damien_The_Unbeliever has answered your main question.