Views and functions
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A view is a virtual table that contains data from one or more real tables but appears as its own table. Views can be used to restrict access to columns, combine columns from different tables, and simplify complex queries. User defined functions allow custom functions to be created that can take in parameters and return values. They are compiled and executed at runtime and can be called from queries and other functions. An example function is provided that returns the number of jobs applied for by a given person by querying a jobs table.
Views and functions
- 2. VIEWSAND USER DEFINED FUNCTION Arun RJ [email protected] Facebook Profile TwitterProfile www.linkedin.com/arunrj
- 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. VIEWS A view is a virtual table. In SQL, a view is a virtual table based on the result-set of an SQL statement. 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.
- 5. SYNTAX OF VIEW CREATE VIEW view_name AS SELECT column_name(s) FROM table_name WHERE condition Example… Int_std_id Vchr_std_name Int_std_age Vchr_std_city 1 amal 12 calicut 2 arun 13 cochin 3 rahul 13 kollam 4 raju 12 kottayam
- 6. Create view vw_tbl_std as select int_std_id,vchr_std_name from tbl_std; Int_std_id Vchr_std_name 1 amal 2 arun 3 rahul 4 raju
- 7. You can modify the definition of a view by the following syntax alter view view_name as select coloumn name from table name; Example… alter view vw_tbl as select std_age from tbl_std; the above query will alter the previous view as below std_age 12 13 13 12
- 8. User Defined Functions In mysql A function is a group of statements that executes upon request SQL provides many built in function and allow us to define user defined function A request to execute a function is called a function call When a function is called it should pass arguments that specify data upon which the function perform its computation
- 9. 1. User defined functions can pass input parameters 2. user defined functions are compiled and executed at run time,so it is slower than stored procedure 3. user defined functions can’t return deterministic values like getdate() 4. stored procedure cannot be called from inside a user defined function where as a stored procedure can call user defined function and can call another stored procedure inside it
- 10. The define statement… CREATE FUNCTION function_name(parameters) RETURNS(return_data type) { statements; }
- 11. Example… DELIMITER // CREATE FUNCTION fn_getvalue( name varchar(20)) RETURNS float DETERMINISTIC READS SQL DATA BEGIN DECLARE value float; SET value=45; IF name='amal' THEN SET value=8.5; END IF; RETURN value; END//
- 12. mysql> select fn_getvalue('amal'); Select fn_getvalue(‘amal’); //function call +---------------------+ | fn_getvalue('amal') | +---------------------+ | 8.5 | +---------------------+ 1 row in set (0.00 sec)
- 13. Example… delimiter // CREATE FUNCTION fn_getdeliveryprice2 (p_country Varchar(50), p_city Varchar(50)) RETURNS Float DETERMINISTIC READS SQL DATA BEGIN DECLARE v_price Float; SET v_price = 45; IF p_country = 'iceland' THEN IF p_city='warhan' THEN SET v_price=8.15; ELSE SET v_price=7.15; END IF; END IF; RETURN v_price; END//
- 14. Problem-create a user defined function to find no of jobs applied by a person DELIMITER // CREATE FUNCTION fn_no_of_job3(vchr_a varchar(100)) RETURNS int DETERMINISTIC READS SQL DATA BEGIN DECLARE s int; select int_no_of_jobs_applied into s from tbl_jobs2 where vchr_user_name=vchr_a; RETURN s; END // DELIMITER// select fn_no_of_job3(‘amal’);
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