Wednesday, March 21, 2007

SQL Tips - Some useful UDF for SQL Server 2000

Introduction
UDF examples
  • Database creation date
  • Date the object was created
  • Get date part of datetime value
  • Get time part of datetime value
  • Get the number of working days between two dates

    • 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, which 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

    Here you can find some useful user-defined functions.

    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')

    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')

    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')

    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')

    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 <> 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')
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