All 7 Constraints (Primary Key, Foreign Key, Check & Unique) questions
More in Constraints (Primary Key, Foreign Key, Check & Unique)
What is a primary key constraint, and why is it important for a database table? What is a foreign key constraint, and how does it help maintain data integrity between two related tables? What is a check constraint, and how do you use one to enforce a specific business rule at the database level? How is a unique constraint different from a primary key constraint, and when would you use one instead of the other? How do cascading actions work with foreign key constraints, such as ON DELETE CASCADE, and what risks come with using them? How would you add a new constraint to an existing table that already contains data, especially if some existing rows might violate that constraint?
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SQL Server › Constraints (Primary Key, Foreign Key, Check & Unique)

How do you temporarily disable a constraint to perform a bulk data load, and how do you safely re-enable it afterward?

Intermediate

Answer

You use ALTER TABLE with the NOCHECK CONSTRAINT option to temporarily disable a specific constraint, perform your bulk data operation, and then re-enable it using CHECK CONSTRAINT, ideally with the WITH CHECK option to also validate that all the newly loaded data actually satisfies the constraint.
ALTER TABLE Orders NOCHECK CONSTRAINT FK_Orders_Customers;
-- Perform bulk insert here
ALTER TABLE Orders WITH CHECK CHECK CONSTRAINT FK_Orders_Customers;
Real-world example A data migration team temporarily disables a foreign key constraint to quickly bulk load historical order data, then re-enables and validates the constraint afterward to confirm all the loaded data is actually consistent.

Common follow-ups: What is the performance benefit of disabling constraints during a bulk load?;How do you find out if a constraint is currently trusted or untrusted after being re-enabled?

Query Optimization & Plans;Data Types & Schema Design
All 7 Constraints (Primary Key, Foreign Key, Check & Unique) questions