t-sql

You can use the code below to disable all CHECK and foreign key constraints for the current database in SQL Server.

EXEC sp_MSforeachtable @command1="ALTER TABLE ? NOCHECK CONSTRAINT ALL"

This uses Microsoft’s undocumented sp_MSforeachtable stored procedure. This procedure allows you to perform tasks against each table in a database. So it’s perfect for our task here – to disable all CHECK constraints within the current database.

Below is an example where I do this and then check the result.

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You can use the code below to enable all CHECK and foreign key constraints for the current database in SQL Server.

When you enable a CHECK or foreign key constraint, you have the option of checking existing data in the table before the constraint is enabled. Doing this allows you to verify whether or not any existing violates the constraint. To perform this check, use WITH CHECK within the code, otherwise use WITH NOCHECK.

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You can use the code below to disable all CHECK and foreign key constraints for a specific table in SQL Server.

Just replace TableName with the name of the applicable table.

ALTER TABLE TableName NOCHECK CONSTRAINT ALL

Below is an example where I do this and then check the result.

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You can use the code below to enable all CHECK and foreign key constraints for a specific table in SQL Server.

When you enable a constraint in SQL Server, you need to decide whether it should check any existing data or not. This is an important consideration if the table already contains data, because that existing data may potentially violate the constraint’s rules.

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When you attempt to enter data into a table that has a fully enabled CHECK constraint, you will only be successful if the data doesn’t violate that constraint. If you attempt to enter invalid data, the operation will fail with an error.

But what if you find yourself in the situation where you really must insert data that will violate the CHECK constraint? Perhaps the constraint no longer applies, or maybe you have an exception where one row is allowed to bypass the constraint. Either way, you won’t be able to enter anything outside the rules of the constraint.

If you find yourself in this situation, you can always disable the constraint. Here’s how to do that using Transact-SQL.

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If you have a CHECK constraint in SQL Server that is currently disabled, you can use the code below to re-enable it.

When you enable a CHECK constraint (or a foreign key constraint for that matter), you have the option to specify whether or not to check any existing data in the table.

Below are code examples of enabling a CHECK constraint, while specifying each of these different options.

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In SQL Server you can create a CHECK constraint in a table to specify the data values that are acceptable in one or more columns.

If a table has a CHECK constraint on it, and you try to provide data that doesn’t conform to the CHECK constraint, the operation will fail with an error.

This helps to maintain data integrity, because it helps to prevent invalid data from entering the database.

When you create a CHECK constraint, you provide a logical expression that returns TRUE or FALSE. This logical expression is what’s used to check the data.

CHECK constraints are similar to foreign key constraints because they control the values that are put in a column. However, the difference is in how they determine which values are valid: Foreign key constraints obtain the list of valid values from another table, while CHECK constraints determine the valid values from a logical expression.

Constraints can be defined at the column level or table level. A column-level constraint applies to just the data in that column. A table-level constraint applies to the whole row, and checks data from multiple columns.

Below are examples of creating both column-level and table-level CHECK constraints.

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