Search code examples
sqlsql-servert-sqldefault-constraint

Command for adding a default constraint

There appears to be at least two ways to add a default constraint using straight T-SQL. Am I correct that the only difference between the two below is that the second method specifically creates a name for the constraint, and the first method has one generated by SQL Server?

ALTER TABLE [Common].[PropertySetting] ADD DEFAULT ((1)) FOR [Active];
ALTER TABLE [Common].[PropertySetting] ADD CONSTRAINT [DF_PropertySetting_Active) DEFAULT ((1)) FOR [Active];
Solution

  • Pretty much, yes for an ALTER TABLE

    You can add a columnn with default in one step for CREATE or ALTER too.

    ALTER TABLE dbo.TableName
    ADD bar varchar(100) CONSTRAINT DF_Foo_Bar DEFAULT ('bicycle');

ALTER TABLE dbo.TableName
    ADD bar varchar(100) DEFAULT ('bicycle');

    As you noted, the system generates a name if one is not supplied. CONSTRAINT constraint_name is optional says MSDN. The same applies to any column or table CONSTRAINT

    If the column was already created, and you only want to add a (named) DEFAULT constraint, then use:

    ALTER TABLE dbo.TableName
    ADD CONSTRAINT DF_Foo_Bar DEFAULT 'bicycle' FOR FieldName;

    To have the system generate the DEFAULT constraint name (which will be of the form DF_{TableName}_{Column}_{8RandomChars}, e.g. DF_TableName_FieldName_12345678) then omit the CONSTRAINT <name> part, like so:

    ALTER TABLE dbo.TableName
    ADD DEFAULT 'bicycle' FOR FieldName;