Create Check Constraints

THIS TOPIC APPLIES TO:yesSQL Server (starting with 2008)yesAzure SQL DatabasenoAzure SQL Data Warehouse noParallel Data Warehouse

You can create a check constraint in a table to specify the data values that are acceptable in one or more columns in SQL Server 2017 by using SQL Server Management Studio or Transact-SQL.

In This Topic

Before You Begin

Security

Permissions

Requires ALTER permissions on the table.

Using SQL Server Management Studio

To create a new check constraint

  1. In Object Explorer, expand the table to which you want to add a check constraint, right-click Constraints and click New Constraint.

  2. In the Check Constraints dialog box, click in the Expression field and then click the ellipses (…).

  3. In the Check Constraint Expression dialog box, type the SQL expressions for the check constraint. For example, to limit the entries in the SellEndDate column of the Product table to a value that is either greater than or equal to the date in the SellStartDate column or is a NULL value, type:

    SellEndDate >= SellStartDate OR SellEndDate IS NULL  
    

    Or, to require entries in the zip column to be 5 digits, type:

    zip LIKE '[0-9][0-9][0-9][0-9][0-9]'  
    
    Note

    Make sure to enclose any non-numeric constraint values in single quotation marks (').

  4. Click OK.

  5. In the Identity category, you can change the name of the check constraint and add a description (extended property) for the constraint.

  6. In the Table Designer category, you can set when the constraint is enforced.

    To: Select Yes in the Following Fields:
    Test the constraint on data that existed before you created the constraint Check Existing Data On Creation Or Enabling
    Enforce the constraint whenever a replication operation occurs on this table Enforce For Replication
    Enforce the constraint whenever a row of this table is inserted or updated Enforce For INSERTs And UPDATEs
  7. Click Close.

Using Transact-SQL

To create a new check constraint

  1. In Object Explorer, connect to an instance of Database Engine.

  2. On the Standard bar, click New Query.

  3. Copy and paste the following example into the query window and click Execute.

    ALTER TABLE dbo.DocExc   
       ADD ColumnD int NULL   
       CONSTRAINT CHK_ColumnD_DocExc   
       CHECK (ColumnD > 10 AND ColumnD < 50);  
    GO  
    -- Adding values that will pass the check constraint  
    INSERT INTO dbo.DocExc (ColumnD) VALUES (49);  
    GO  
    -- Adding values that will fail the check constraint  
    INSERT INTO dbo.DocExc (ColumnD) VALUES (55);  
    GO  
    

    For more information, see ALTER TABLE (Transact-SQL).