This document discusses user defined functions (UDF) and views in MySQL. It provides the syntax for creating UDFs and views. UDFs allow users to define reusable functions that can be called from queries. Views act as virtual tables that are based on the result set of a SELECT statement. The document provides an example of creating a UDF to return the number of jobs applied by a user and an example of creating a view from an employee table to select employee IDs and names. It describes some key properties and limitations of UDFs and how views can be used to rename attributes and insert/delete data.

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USER DEFINED FUNCTIONS AND VIEWS
IN MYSQL

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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;

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