Constraints make a bad performance, but why?

Hi all,

why do constraints make a bad performance for loading data in the Data Warehouse? why have they to be disabled while the ETL-Process runs?.

I would appreciate any answer...

Best Regards

I assume you are referring to foreign and primary key constraints... because it requires the database to perform one or more queries every time a row is added.

If you are inserting a row that contains a foreign key with a constraint, the DB must locate the row in the table that the FK is referencing. However, if you are using surrogate key assignment, your ETL code has already handled the check, making the FK constraint redundant.