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USER DEFINED FUNCTIONS AND VIEWS
IN MYSQL

3. Disclaimer: This presentation is prepared by trainees of
baabtra.com as a part of mentoring program. This is not
official document of baabtra.com – Mentoring Partner

4. User Defined functions (UDF)
• It is the SQL routines used to encapsulate program logic.
• A function is a set of codes written to perform certain
task.

5. • UDF cant call a Stored Procedure.
• Functions are compiled and executed at run time thus it
slower than stored procedure.

6. Syntax : creating a UDF
DELIMITER //
CREATE FUNCTION function_name (parameter datatype) RETURNS datatype
BEGIN
<statements>
............
............
END //
DELIMITER ;
Syntax : Calling a function
SELECT function_name(parameter);

7. E.g. :
DELIMITER //
CREATE FUNCTION fun_checkNum(int_x int) RETURNS varchar(20) NO SQL
BEGIN
DECLARE numtype varchar(25);
IF(int_x<0) THEN
SET numtype='Negative Number';
ELSE
SET numtype='Positive Number';
END IF;
RETURN numtype;
END //
DELIMITER;
//Calling Function and output :
mysql> SELECT fun_checkNum(-1);
+------------------+
| fun_checkNum(-1) |
+------------------+
| Negative Number |
+------------------+

8. PECULIARITIES OF USER DEFINED FUNCTIONS
• UDF are compiled and Executed at run time.
• UDF must return a value.
• UDF can only have input parameters.
• UDF can be called from stored procedure.
• A UDF can call another UDF.
• UDF allows only SELECT command in it, no other DML,DDL,DCL
commands.

9. Problem1:
Write a user defined function to return how many jobs applied by
a user.
DELIMITER //
CREATE FUNCTION fun_jobsApplied(getID int) RETURNS int READS SQL DATA
BEGIN
DECLARE count int;
SELECT int_jobs_applied into count FROM tbl_jobs where int_id=getID;
RETURN count;
END //
DELIMITER ;
SELECT fun_jobsApplied(1); //calling udf, it returns number of applied jobs
corresponding to id=1

10. Views in Mysql

11. Views
• In SQL, a VIEW is a virtual relation based on the result
set of a SELECT statement.
• A view can be considered as a stored query or a virtual table.
• A view contains rows and columns, just like a real table.
The fields in a view are fields from one or more real tables in
the database.
• View Doesn't take any storage space.

12. Syntax:
CREATE VIEW view_name AS
SELECT column_name(s)
FROM table_name
WHERE condition;

13. pk_int_emp_id vchr_emp_name vchr_company
1 James Dell
2 John Sony
3 Albert Hp
CREATE VIEW vw_tbl_employee AS
SELECT pk_int_emp_id , vchr_emp_name FROM tbl_employee;
SELECT * FROM vw_tbl_employee; //to see all content of view
E.g. VIEW
Creating a view for below table
pk_int_emp_id vchr_emp_name
1 James
2 John
3 Albert

14. Renaming Attributes in View
• Sometime, we might want to distinguish attributes by giving the
different name from names in table .
CREATE VIEW vw_tbl_employee (Employeeid,EmployeeName) AS
SELECT pk_int_emp_id , vchr_emp_name FROM tbl_employee;
SELECT * FROM vw_tbl_employee;
Employeeid EmployeeName
1 James
2 John
3 Albert

15. Insert values to view
We can insert value into view as same as that of table
INSERT INTO vw_tbl_employee (Employeename) VALUES
(‘Smith’);
Employeeid EmployeeName
1 James
2 John
3 Albert
4 Smith

16. Delete from view
DELETE FROM vw_tbl_employee WHERE Employeeid=1;
Employeeid EmployeeName
2 John
3 Albert
4 Smith
DROP VIEW
DROP VIEW viewname;
DROP VIEW vw_tbl_employee;

17. Thank you...

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