User defined Function in SQL

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baabtra as a part of mentoring program. This is not official
document of baabtra –Mentoring Partner
Baabtra-Mentoring Partner is the mentoring division of baabte System Technologies Pvt .
Ltd

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5. User Defined Functions In SQL
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6. What is UDF?
• User defined functions are similar to ordinary functions
found in programming languages.
• The main purpose of UDF is code reusability.

7. Benefits of using UDF
• Modular programming.
• Faster execution.
• Code reusability.

8. • User defined functions can be passed input parameters
• User defined functions are compiled and executed at
runtime so pretty slower than stored procedures
• UDF can’t perform DML (data manipulation language)
operations like Insertion, Update and Deletion on the base
table
• UDF can’t return non deterministic values like GETDATE ()
etc
• Stored procedure can’t be called from inside a UDF whereas
a stored procedure can call a user defined function or another
stored procedure inside it

9. Types of UDF…
• Scalar functions
• Returns a single value
• Inline functions
• Returns a table
• Table values functions
• Multiple operations, complex logic just like Stored
procedures

10. FORMAT OF A UDF
CREATE FUNCTION dbo.function_name
(
@parameter1 datatype = default value,
@parameter2 datatype
)
RETURNS datatype
AS
BEGIN
sql statements foms function body ...
RETURN value
END

12. SCALAR FUNCTION
CREATE FUNCTION dbo.teach_name(@teachr_id int)
RETURNS varchar(20)
AS
BEGIN
Declare @returnvalue varchar(20)
Select @returnvalue=teacher_name from tbl_teachers where
teacher_id=@teachr_id
RETURN @returnvalue
END
Execution: select dbo.teach_name(1002)as teacher_name

14. INLINE FUNCTION
CREATE FUNCTION dbo.list_teach(@name varchar(10))
RETURNS TABLE
AS
RETURN SELECT *
FROM tbl_teachers where teacher_name like '%'+@name+'%'
Execution: select * from dbo.list_teach('i')

16. Table values functions
CREATE FUNCTION udf_teach_day()
RETURNS @Result TABLE
(
vchr_teacher_name varchar(20)
,vchr_day varchar(10)
)
AS
BEGIN
INSERT INTO @Result
(vchr_teacher_name,vchr_day)
select teacher_name,datepart(dw,teacher_doj)as vchr_day from tbl_teachers
UPDATE @Result
SET vchr_day = 'weekday' where vchr_day<>cast(2 as varchar(20))
UPDATE @Result
SET vchr_day = 'monday' where vchr_day=cast(2 as varchar(20))
RETURN
END

17. Execution:Select * from udf_teach_day()

19. Conclusion
UDF are similar to functions in the programming languages, they provide
a mechanism for extending the functionality of the database server by
adding a function that can be evaluated in SQL statements.

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