You can not alter constraints ever but you can drop them and then recreate. Have look on this. ALTER TABLE your_table DROP CONSTRAINT ACTIVEPROG_FKEY1; and then recreate it with ON DELETE CASCADE like this. ALTER TABLE your_table add CONSTRAINT ACTIVEPROG_FKEY1 FOREIGN KEY(ActiveProgCode) REFERENCES PROGRAM(ActiveProgCode) ON DELETE CASCADE;

Constraints are used to limit the type of data that can go into a table. This ensures the accuracy and reliability of the data in the table. If there is any violation between the constraint and the data action, the action is aborted. Constraints can be column level or table level.

May 3, 2012 · You can't update a constraint in SQL Server at least. ALTER TABLE SomeTable DROP CONSTRAINT gradeRule In addition, you'll need to update the table data before adding the new constraint, so that it meets the new constraint.

SQL ALTER TABLE Statement. The ALTER TABLE statement is used to add, delete, or modify columns in an existing table. The ALTER TABLE statement is also used to add and drop various constraints on an existing table.

Feb 4, 2025 · To modify a UNIQUE constraint using Transact-SQL, you must first delete the existing UNIQUE constraint and then re-create it with the new definition. For more information, see Delete Unique Constraints and Create Unique Constraints.

Mar 28, 2011 · Modifying a constraint is documented, but the specific type of change you're looking for is not documented. Only changing the constraint state is allowed. e.g. enable, disable, validate, etc. constraint Employee_fk foreign key(gender) references Gender_Long(id));

Jul 11, 2023 · Databases have five core constraints: check, not null, unique, primary keys, and foreign keys. Defining these helps improve data quality. The challenge comes if you want to update an existing constraint. For example: How do you alter the search condition for a check constraint? Or modify the columns in a unique constraint?

Jan 30, 2025 · It allows you to add, remove, or modify columns, change data types, or apply constraints to improve data integrity and ensure that the table meets evolving business requirements. It allows for structural changes like adding new columns, modifying existing ones, deleting columns, and renaming columns within a table.

Feb 27, 2025 · Once we set a constraint in SQL, we can’t alter it. However, we can replace it with a constraint with different options. So, we first drop the old constraint and add a new one: To drop a constraint, we first need to find its name. Here’s how we can list all constraints for a table: FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS.

Apr 24, 2011 · We can prevent constraints……. create table x (id int not null, salary money not null constraint check_sale check(salary>0)) select * from x insert into x values (1,-8) alter table x nocheck constraint check_sale