How To Provide Default Values to Function Parameters in SQL Server Transact-SQL?

If you add a parameter when creating a stored procedure, you can provide a default value so that the execution statement is not required to pass input value to this parameter:

• To define a default value to a parameter when creating the function, you should use this format: "@parameter_name data_type = default_value".
• To use the default value of a parameter when executing the function, you should use the keyword DEFAULT as the input value for that parameter.

The tutorial exercise below shows you how provide default values to function parameters:

USE FyiCenterData;
GO

CREATE FUNCTION Age_In_Days (
   @birth_date DATETIME,
   @today DATETIME = NULL
   )
   RETURNS INT
AS BEGIN
   IF @today IS NULL SET @today = GETDATE();
   RETURN DATEDIFF(DAY, @birth_date, @today);
END;
GO

-- Default value is used
PRINT 'Age in days: '+STR(
   dbo.Age_In_Days('01-Jan-2007', DEFAULT));
GO
Age in days:        138

-- Default value is not used
PRINT 'Age in days: '+STR(
   dbo.Age_In_Days('01-Jan-2007', '11-May-2007'));
GO
Age in days:        130

-- Can not skip input values 
-- even for parameters with default values
PRINT 'Age in days: '+STR(
   dbo.Age_In_Days('01-Jan-2007'));
GO
Msg 313, Level 16, State 2, Line 1
An insufficient number of arguments were supplied 
for the procedure or function dbo.Age_In_Days.

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