1. CSCI 2141 – Intro to Database Systems
Advanced SQL – Stored Procedures

2. Stored Procedures (SP)
Named collection of procedural and SQL statements
Stored in the database – just like triggers
Can be used to encapsulate and represent business transactions
E.g. creating a SP to represent a product sale, or addition of a new customer
In scenarios where you need to update many tables simultaneously, stored procedures may help?

3. Advantages of Stored Procedures
Advantages of SP
Reduced network traffic
No transmission of individual SQL statements over the network
Increased performance
All transactions are executed locally on the server
Encapsulation and security
Column names of the table are hidden, and execution privileges to users can be granted
Change in table structure will not affect code
Only the number of variables passed may change

4. Stored Procedure – Syntax
CREATE [OR REPLACE] PROCEDURE procedure_name [(argument [IN/OUT] data-type, … )]
[IS/AS] [variable_namedata type[:=initial_value]]
BEGIN
SQL (or procedural) statements; …
END
Arguments – specify the parameters passed to the SP
IN/OUT – whether parameter is for input, output or both
Variables can be declared between the IS and BEGIN keywords

5. SP – Business Case
MySQL
SalesCo wants to provide an additional 5% discount for all PRODUCTs when the quantity on hand (P_QOH) is more than or equal to twice the minimum quantity (P_MIN)
MySQL
delimiter // CREATE PROCEDURE PRC_PROD_DISCOUNT (IN disc DECIMAL) BEGIN UPDATE PRODUCT SET P_DISCOUNT = P_DISCOUNT + disc/ WHERE P_QOH >= P_MIN*2;
END;//
CALL PRC_PROD_DISCOUNT(5);
Advantage is that your manager doesn’t need to be an SQL expert to be able to provide a 10% discount. She can simply call the procedure with the correct amount
Also, you can pass values to stored procedures. Hence one method of writing interfaces is to create SPs in database and your application can simply call those SPs with values

6. Business Case 2 – Add a New Customer
MySQL
For MySQL
DELIMITER // CREATE PROCEDURE PRC_CUS_ADD (IN w_ln VARCHAR(20), IN w_fn VARCHAR(20), IN w_init VARCHAR(20), IN w_ac VARCHAR(20), IN w_ph VARCHAR(20))
BEGIN
DECLARE c_code INT;
SELECT MAX(CUS_CODE) INTO c_code FROM CUSTOMER;
INSERT INTO CUSTOMER (CUS_CODE, CUS_LNAME, CUS_FNAME, CUS_INITIAL, CUS_AREACODE, CUS_PHONE) VALUES (c_code+1, W_LN, w_fn, w_init, w_ac, w_ph); END;//
Advantages:
Actual column names are hidden (encapsulated)
Only need to call procedure and enter values to insert a customer (expertise in SQL not required)
Any changes in table structure do not need change in code (only addition or removal of values from the call)

7. Exercise
Table: SPECIES
Table: ANIMAL
SP_ID
DESCRIP 1
INSECT 2
BIRD 3
FISH 4
MAMMAL ID
NAME
SP_ID
LIFE_EXP 1
Cat 4 20 2
Elephant 70 3
Trout 5
Shark 25
Canary 6
Albatross 40 7
Swift
Write a procedure named PRC_SP_ANIM_ADD that accepts two parameters –description of a species and name of an animal – and inserts a row in the Category and Animal table with appropriate values.

8. Solution
delimiter // CREATE PROCEDURE PRC_SP_ANIM_ADD (IN sp_desc varchar(45), IN an_desc varchar(45)) BEGIN DECLARE spid INT(11); DECLARE anid INT(11); SELECT MAX(sp_id) INTO spid FROM species; INSERT INTO species VALUES (spid, sp_desc); SELECT MAX(id) INTO anid FROM animal; INSERT INTO animal (id, name, sp_id) VALUES (anid, an_desc, spid); END;// call PRC_SP_ANIM_ADD("INSECT", "ANT");

9. Solution – Spot the Logical Error
delimiter // CREATE PROCEDURE PRC_SP_ANIM_ADD (IN sp_desc varchar(45), IN an_desc varchar(45)) BEGIN DECLARE spid INT(11); DECLARE anid INT(11); SELECT MAX(sp_id) INTO spid FROM species; INSERT INTO species VALUES (spid, sp_desc); SELECT MAX(id) INTO anid FROM animal; INSERT INTO animal (id, name, sp_id) VALUES (anid, an_desc, spid); END;// call PRC_SP_ANIM_ADD("INSECT", "ANT");
Error
PK already exists

10. Corrected Solution
delimiter // CREATE PROCEDURE PRC_SP_ANIM_ADD (IN sp_desc varchar(45), IN an_desc varchar(45)) BEGIN DECLARE spid INT(11); DECLARE anid INT(11); SELECT MAX(sp_id) INTO spid FROM species; INSERT INTO species VALUES (spid+1, sp_desc); SELECT MAX(id) INTO anid FROM animal; INSERT INTO animal (id, name, sp_id) VALUES (anid+1, an_desc, spid+1); END;// call PRC_SP_ANIM_ADD("INSECT", "ANT"); What if the species already exists in the SPECIES table?

11. Corrected Solution 2
delimiter // CREATE PROCEDURE PRC_SP_ANIM_ADD (IN sp_desc varchar(45), IN an_desc varchar(45)) BEGIN DECLARE spid INT(11); DECLARE anid INT(11); IF EXISTS (SELECT sp_id FROM species WHERE descrip = sp_desc) THEN SELECT sp_id INTO spid FROM species WHERE descrip = sp_desc; ELSE SELECT MAX(sp_id) INTO spid FROM species; INSERT INTO species VALUES (spid+1, sp_desc); END IF; SELECT MAX(id) INTO anid FROM animal; INSERT INTO animal (id, name, sp_id) VALUES (anid+1, an_desc, spid+1); END;// call PRC_SP_ANIM_ADD("INSECT", "ANT");