The constraint_keys column shows the default constraint definition. We can use the sp_helpconstraint stored procedure to view the list of constraints created on the table: EXEC Sp_helpconstraint 'SalesDetails' The following query populates the list of default constraints and their definitions: SELECT NAME , You can see the two constraints named DF_SalesDetails_SaleQty and DF_SalesDetails_ProductName created.Īnother way to view constraints by querying sys.default_constraints. Open SSMS and expand Databases > DemoDatabase > SalesDetails > Constraint: We can view the list of the DEFAULT constraint using SQL Server Management Studio and querying dynamic management views. Viewing the DEFAULT Constraint Using SSMS Run the SELECT statement to view the data from the SalesDetails table: USE demodatabaseĪs you can see, the value of the Product_name column is Not Applicable. Now, let us insert a record without specifying the product name: INSERT INTO salesdetails When the constraint is dropped, run the query to create the constraint: ALTER TABLE dbo.salesdetailsĪDD CONSTRAINT df_salesdetails_productname DEFAULT 'Not Applicable' FOR Execute the following query: ALTER TABLE dbo.salesdetailsĭROP CONSTRAINT df_salesdetails_productname First, we must drop the DF_SalesDetails_ProductName constraint. Suppose, instead of inserting N/A, we want to insert Not Applicable. We can change the definition of the default constraint: first, drop the existing constraint and then create the constraint with a different definition. Modifying the DEFAULT Constraint using T-SQL Scripts Once the record is inserted, run the SELECT query to view the data: USE demodatabaseĪs you can see in the above image, the value of the Product_name column for PROD0003 is N/A. Insert a record without specifying the product name: INSERT INTO salesdetails Now, let us observe the constraint behaviour. The following query creates a default constraint: ALTER TABLE dbo.salesdetailsĪDD CONSTRAINT df_salesdetails_productname DEFAULT 'N/A' FOR product_name To do that, I am creating a default constraint named DF_SalesDetails_ProductName on the Product_name column. We insert the data into the table without specifying the Product_name column value. When we do not specify the value of the column_name in the INSERT statement, it inserts the value specified in the default_value parameter.įirst, let us add the Product_name column into SalesDetails: ALTER TABLE salesdetails default_value: specify the value that you want to insert – an integer, character, or character string.column_name: specify the name of the column where you want to create the default constraint. ![]() constraint_name: specify the desired constraint name.tbl_name: specify the name of the table where you want to add the default constraint.To add a constraint on an existing column of the table, we use the ALTER TABLE ADD CONSTRAINT statement: ALTER TABLE ĪDD CONSTRAINT DEFAULT FOR Adding a DEFAULT Constraint Into Existing Table SQL Server has created a constraint with the system-generated name. Run the following script to view the constraint name: SELECT NAME , SQL Server creates a constraint with a system-generated unique name.Ĭreate the table using the below query: USE demodatabase While creating a table, we do not specify the name of the DEFAULT constraint. Use the following query to view data from the table: INSERT INTO salesdetailsĪs you can see, the zero has been inserted into the Sale_Qty column. ![]() Execute the following query: INSERT INTO salesdetails Now, let us test the constraint behavior by inserting some dummy records into it. ![]() Sale_qty INT CONSTRAINT df_salesdetails_saleqty DEFAULT 0 To do that, I am creating a default constraint named DF_SalesDetails_SaleQty on the Sale_Qty column. When we insert data into the table without specifying the Sale_Qty column value, the query must insert zero. Adding a DEFAULT Constraint While Creating a New Table To create a default constraint, you need the ALTER TABLE and CREATE TABLE permission. When we execute the INSERT statement but do not specify any value for the column with the default constraint created, SQL Server inserts the default value specified in the DEFAULT constraint definition. What is DEFAULT CONSTRAINT in SQL Server?Ī default constraint specifies the default value for the column.
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