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What are the constraints for a column in SQL?
Constraints can be column level or table level. Column level constraints apply to a column, and table level constraints apply to the whole table. The following constraints are commonly used in SQL: PRIMARY KEY – A combination of a NOT NULL and UNIQUE.
How to add unique constraint to combination of two columns?
I have a table and, somehow, the same person got into my Person table twice. Right now, the primary key is just an autonumber but there are two other fields that exist that I want to force to be unique. I only want 1 record with a unique PersonNumber and Active = 1.
How are unique constraints referenced in SQL Server?
A UNIQUE constraint can be referenced by a FOREIGN KEY constraint. When a UNIQUE constraint is added to an existing column or columns in the table, by default, the Database Engine examines the existing data in the columns to make sure all values are unique.
How to write check constraint on two columns?
I have a table in SQL Server with two numeric columns. At least one of these numeric fields must be filled. How do I write a check constraint to verify this?
How to restrict the length of integer when creating a table in SQL?
When creating a table in SQL SERVER, I want to restrict that the length of an INTEGER column can only be equal 10. eg: the PhoneNumber is an INTEGER, and it must be a 10 digit number.
When do constraints apply to the whole 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. Column level constraints apply to a column, and table level constraints apply to the whole table. PRIMARY KEY – A combination of a NOT NULL and UNIQUE.
How to limit the number of rows in a table?
Create a helper table CheckFiveRows with column ID that contains five rows with values 1 to 5. ID is the primary key. Make sure that it contains only five rows.