To add a constraint to an existing table use the alter table statement with the add constraint command. There are four different types of constraints:
- Primary Key Constraints – Enforces unique values for specified column, can be referenced.
- Foreign Key Constraints – Enforces a reference to a primary key
- Unique Constraints – Ensures unique values within a column
- Check Constraints – Limits values acceptable for a column based on an evaluation
Add unique constraint
ALTER TABLE dbo.Presidents ADD CONSTRAINT President_unique UNIQUE (President)
Add constraint to test value
ALTER TABLE dbo.Presidents ADD CONSTRAINT President_unique CHECK (YearsInOffice >= 0 AND YearsInOffice < 13)
Popular search terms:
whic tag is used to add columns in a table
can i alter the order of the columns in a table
Hi, unfortunately you cannot. You have to drop and recreate the table.