Introduction
SQL Server 2000 supports User-Defined Functions (UDFs) - one or more
Transact-SQL statements that can be used to encapsulate code for reuse.
User-defined functions cannot make a permanent changes to the data or
modify database tables. UDF can change only local objects for this UDF,
such as local cursors or variables.
There are three types of UDF in SQL Server 2000:
- Scalar functions
- Inline table-valued functions
- Multistatement table-valued functions
Scalar functions return a single data value (not a table)
with RETURNS clause. Scalar functions can use all scalar
data types, with exception of timestamp and user-defined data types.
Inline table-valued functions return the result set of a single
SELECT statement.
Multistatement table-valued functions return a table, that was
built with many TRANSACT-SQL statements.
User-defined functions can be invoked from a query like built-in
functions such as OBJECT_ID, LEN, DATEDIFF, or can be executed
through an EXECUTE statement like stored procedures.
UDF examples
Database creation date
This UDF will return the creation date for a given database (you should
specify database name as parameter for this UDF):
CREATE FUNCTION dbo.DBCreationDate( @dbname sysname )
RETURNS datetime
AS
BEGIN
DECLARE @crdate datetime
SELECT @crdate = crdate FROM master.dbo.sysdatabases
WHERE name = @dbname
RETURN ( @crdate )
END
GO
This is the example for use:
SELECT dbo.DBCreationDate('pubs')
GO
Date the object was created
This UDF will return the creation date for a given object in the
current database:
CREATE FUNCTION dbo.ObjCreationDate( @objname sysname)
RETURNS datetime
AS
BEGIN
DECLARE @crdate datetime
SELECT @crdate = crdate FROM sysobjects WHERE name = @objname
RETURN ( @crdate )
END
GO
This is the example for use:
SELECT dbo.ObjCreationDate('authors')
GO
Get date part of datetime value
This UDF will return the date part of datetime value:
CREATE FUNCTION dbo.DatePart( @fDate datetime )
RETURNS varchar(10)
AS
BEGIN
RETURN ( CONVERT(varchar(10),@fDate,101) )
END
GO
This is the example for use:
SELECT dbo.DatePart('11/11/2000 11:15AM')
GO
Get time part of datetime value
This UDF will return the time part of datetime value:
CREATE FUNCTION dbo.TimePart( @fDate datetime )
RETURNS varchar(10)
AS
BEGIN
RETURN ( CONVERT(varchar(7),right(@fDate,7),101) )
END
GO
This is the example for use:
SELECT dbo.TimePart('11/11/2000 11:15AM')
GO
Get the number of working days between two dates
This UDF will return the number of working days between two dates
(not including these dates):
CREATE FUNCTION dbo.GetWorkingDays( @StartDate datetime,
@EndDate datetime )
RETURNS INT
AS
BEGIN
DECLARE @WorkDays int, @FirstPart int
DECLARE @FirstNum int, @TotalDays int
DECLARE @LastNum int, @LastPart int
IF (DATEDIFF(day, @StartDate, @EndDate) < 2)
BEGIN
RETURN ( 0 )
END
SELECT
@TotalDays = DATEDIFF(day, @StartDate, @EndDate) - 1,
@FirstPart = CASE DATENAME(weekday, @StartDate)
WHEN 'Sunday' THEN 6
WHEN 'Monday' THEN 5
WHEN 'Tuesday' THEN 4
WHEN 'Wednesday' THEN 3
WHEN 'Thursday' THEN 2
WHEN 'Friday' THEN 1
WHEN 'Saturday' THEN 0
END,
@FirstNum = CASE DATENAME(weekday, @StartDate)
WHEN 'Sunday' THEN 5
WHEN 'Monday' THEN 4
WHEN 'Tuesday' THEN 3
WHEN 'Wednesday' THEN 2
WHEN 'Thursday' THEN 1
WHEN 'Friday' THEN 0
WHEN 'Saturday' THEN 0
END
IF (@TotalDays < @FirstPart)
BEGIN
SELECT @WorkDays = @TotalDays
END
ELSE
BEGIN
SELECT @WorkDays = (@TotalDays - @FirstPart) / 7
SELECT @LastPart = (@TotalDays - @FirstPart) % 7
SELECT @LastNum = CASE
WHEN (@LastPart < 7) AND (@LastPart > 0) THEN @LastPart - 1
ELSE 0
END
SELECT @WorkDays = @WorkDays * 5 + @FirstNum + @LastNum
END
RETURN ( @WorkDays )
END
GO
This is the example for use:
SELECT dbo.GetWorkingDays ('11/13/2000', '12/27/2000')
GO
Literature
- SQL Server Books Online
- Super Administrator: Granting Wishes with UDF
http://msdn.microsoft.com/library/periodic/period00/sql00i11.htm
