COP 3718 Intermediate Database Systems. Chapter 13 Stored Procedures

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1 COP 3718 Intermediate Database Systems Chapter 13 Stored Procedures 1

2 Stored Routines A stored procedure is a set of SQL statements stored in a database and made available in the same way we use SQL functions such as count() and avg(). Can be activated/invoked from mysql monitor, from a program, or from another procedure The code in a stored procedure is not part of a program. It is stored in the database catalog When calling stored procedures, we can specify input and output parameters MySQL actually implements two procedural options, which are collectively referred to as stored routines: Stored procedures and Stored Functions 2

3 How MySQL Implements Stored Routine Stored procedures support execution of SQL commands such as SELECT, INSERT, UPDATE, and DELETE can set parameters that can be referenced later from outside of the procedure generally we use stored procedures when we need to work with data found in a database (retrieve rows or insert, update and delete values) 3

4 How MySQL Implements Stored Routine Stored functions support execution only of the SELECT command accept only input parameters, and must return one and only one value a stored function directly be embedded into a SQL command just like we might do with standard MySQL functions such as count() and date_format() we use stored functions to manipulate that data or perform special calculations DROP PROCEDURE procedure_name; DROP FUNCTION function_name; 4

5 Stored Routine Privilege Tables Two tables in the mysql database, proc and procs_priv, are used to manage stored routines and the privileges required to create, execute, alter, and delete them The proc table stores information regarding the stored routine, including its syntax, creation date, parameter list, and more mysql> SELECT db, type, name, definer FROM proc ORDER BY type; The procs_priv table stores privilege information pertinent to which users are allowed to interact with the routines defined in the proc table Note: these tables will be empty/no records if no stored procedures have been created or/and no privileges have been set 5

6 Stored Routine Privilege Tables SHOW DATABASES; USE mysql; SHOW TABLES; SELECT * FROM proc \G; SELECT db, name, type, definer, created FROM proc ORDER BY type; SELECT db, name, type, definer, created FROM proc where name ="test1"; SELECT db, body FROM proc ; The select statement will display records only after a store procedure is created 6

7 Store Procedure Example 1 The procedure in this example : does not receive any parameters a local variable is declared (NUMBER1) with a default value of 100 the procedure has a SELECT statement to display the value of this variable 1. At the mysql monitor prompt, we change the default delimiter to something other than ; mysql> DELIMITER $$ 2. We then create the procedure, preferably in Notepad or any other text editor CREATE PROCEDURE TEST1() BEGIN DECLARE NUMBER1 INTEGER DEFAULT 100; SELECT NUMBER1; END$$ SELECT db, body FROM proc WHERE name ="test1" AND db ="mylibrary"; 7

8 Store Procedure Example 1 (cont.) 3. When done, we can paste these line to mysql monitor to actually create the procedure 4. We should change the delimiter back to the usual ; mysql> DELIMITER ; 5. We can now call the procedure mysql> CALL TEST1() ; 8

9 The DELIMETER By default, MySQL uses the semicolon to determine where a statement ends Stored procedures have several statements, which end with a semicolon We don't want MySQL to do anything until we have finished writing all statements for the stored procedure We need to change the delimiter to a character string different from the semicolon This character string can be pretty much anything (// or $$ or or ^^) Example: DELIMITER $$ 9

10 Store Procedure Example 2 This procedure has a parameter. It receives a number into the variable PRICE The value of PRICE is changed mysql> DELIMITER $$; (Create the procedure in Notepad and then paste it to mysql monitor) CREATE PROCEDURE PRICE_CHANGE(OUT PRICE FLOAT) BEGIN SET PRICE = 200; END$$ mysql> DELIMITER ; 10

11 Store Procedure Example 2 (cont.) Test the procedure by creating a user variable and set it to 100, display the contents using the SELECT command mysql> = 100; mysql> Then, call the procedure and pass the user variable created above, and then display the new value of this variable mysql> CALL PRICE_CHANGE(@PRICE); mysql>

12 Setting Input and Return Parameters Stored procedures can both accept input parameters and return parameters back to the caller For each parameter, we need to declare the name, datatype, and whether it will be used to pass information into the procedure pass information back out of the procedure or both To declare the parameter s purpose, use one of the following three keywords: IN: intended solely to pass information into the procedure. OUT: intended solely to pass information back out of the Procedure INOUT: can pass information into the procedure, have its value changed, and then pass information back out of the procedure. 12

13 Setting Input and Return Parameters (cont.) For any parameter declared as OUT or INOUT, its name needs to have symbol in front of it when calling the stored procedure, so that the parameter can then be called from outside of the procedure Example: a procedure named get_inventory, which accepts two parameters, productid, an IN parameter that determines the product you re interested in, and count, an OUT parameter that returns the value back to the caller s scope: CREATE PROCEDURE get_inventory(in product CHAR(8), OUT count INT)...statements This procedure can then be called this way: CALL get_inventory( Then, the count parameter can be accessed by: 13

14 Declaring and Setting Variables Local variables are often used as temporary placeholders within a stored routine Unlike PHP, MySQL requires that local variables within a stored procedure by explicitly declared before using them Declare the variable with the DECLARE statement Specify a datatype supported by MySQL A default value is optional DECLARE variable_name type [DEFAULT value] Example: we could have a stored procedure named calculate_bonus to calculate a sales person bonus. It might require a variable named sales, and a variable named bonus DECLARE sales DECIMAL(8,2); DECLARE bonus DECIMAL(4,2); 14

15 Declaring and Setting Variables Variable declaration takes place within a BEGIN/END block The declarations must take place before executing any other statements in that block The variable scope is limited to the block in which it s declared It is possible to have several BEGIN/END blocks in a routine Previously used example: CREATE PROCEDURE PRICE_CHANGE(OUT PRICE FLOAT) BEGIN SET PRICE = 200; END$$ The SET statement is used to set the value of a declared stored procedure variable 15

16 Advantages Performance Ease of maintenance Reduction in network bandwidth requirements Security Advantages and Disadvantages Disadvantages May tie you in with a single database vendor Tool support for writing and debugging stored routines is often not as good as for popular programming languages The best advice is always experiment with them before making the decision of implementing them or not 16

17 Advantages of Stored Procedures (cont.) Stored procedures do not depend on a particular host language they can be called from different host languages if multiple languages are used for development, certain common code does not have to be duplicated for each language For example, a specific stored procedure can be called from an online Java application, a batch application written in C a PHP program operating in an Internet environment 17

18 Executing a Stored Routine We reference the stored procedure in conjunction with the CALL statement For example, executing the previously created PRICE_CHANGE stored procedure CALL PRICE_CHANGE(@PRICE); (this was the procedure we created) CREATE PROCEDURE PRICE_CHANGE(OUT PRICE FLOAT) BEGIN SET PRICE = 200; END$$ 18

19 Stored Functions The definition of the CREATE FUNCTION procedure looks very much like that of the stored procedure also starts with a name followed by parameters ends with a body A few differences exist A stored function can have only input parameters, therefore we cannot specify IN, OUT, and INOUT The RETURNS specification follows the parameters and indicates the data type of the value that the stored function returns 19

20 Stored Functions (cont.) Have a strong resemblance to stored procedures code consisting of SQL and procedural statements can be called from applications and SQL statements DELIMITER $$ CREATE FUNCTION hello (s CHAR(20)) RETURNS CHAR(50) DETERMINISTIC RETURN CONCAT('Hello, ',s,'!'); $$ DELIMITER ; SELECT hello("world"); SELECT hello("mary"); 20

21 Stored Functions Example 1 Create a function that counts the number of records in the authors table (mylibrary database) Change the delimiter: DELIMITER $$ Create the function: CREATE FUNCTION NUMBER_OF_AUTHORS() RETURNS INTEGER BEGIN RETURN (SELECT COUNT(*) FROM authors); END$$ Change the delimiter: DELIMITER ; Call the function: SELECT NUMBER_OF_AUTHORS(); 21

22 Stored Functions Example 2 Create a stored function that calculates the number of days between two dates DELIMITER $$ CREATE FUNCTION NUMBER_OF_DAYS (START_DATE DATE, END_DATE DATE) RETURNS INTEGER BEGIN DECLARE DAYS INTEGER; DECLARE NEXT_DATE, PREVIOUS_DATE DATE; SET DAYS = 0; SET NEXT_DATE = START_DATE + INTERVAL 1 DAY; WHILE NEXT_DATE <= END_DATE DO SET DAYS = DAYS + 1; SET PREVIOUS_DATE = NEXT_DATE; SET NEXT_DATE = NEXT_DATE + INTERVAL 1 DAY; END WHILE; RETURN DAYS; END$$ 22

23 Stored Functions Example 2 (cont.) DELIMITER ; SELECT NUMBER_OF_DAYS(' ',' '); Output: NUMBER_OF_DAYS(' ',' ') select number_of_days(' ',' '); Output: number_of_days(' ',' ')

24 Stored Functions Example 2 (cont.) Store the result in a user variable : SELECT NUMBER_OF_DAYS(' ',' ') Display the contents of the variable: Output:

25 Stored Functions Example 3 CREATE FUNCTION shorten(s VARCHAR(255), n INT) RETURNS VARCHAR(255) BEGIN IF ISNULL(s) THEN RETURN ''; ELSEIF n<15 THEN RETURN LEFT(s, n); ELSE IF CHAR_LENGTH(s) <= n THEN RETURN s; ELSE RETURN CONCAT(LEFT(s, n-10), '... ', RIGHT(s, 5)); END IF; END IF; END$$ 25

26 Stored Functions Example 3 (cont.) mysql> SELECT shorten("this is just a test of a very long string", 15); shorten("this is just a test of a very long string", 15) this... tring mysql> SELECT shorten("this is just a test of a very long string", 10); Output: this is ju mysql> SELECT shorten("this is just a test of a very long string", 30); Output: this is just a test... tring 26

27 Stored Functions Example 3 (cont.) mysql> SELECT title, shorten(title, 20) FROM titles LIMIT 10; title shorten(title, 20) nnnn A Guide to the SQL Standard A Guide to... ndard A Programmer's Introduction to PHP 4.0 A Programm... P 4. 0 Alltid den där Annette Alltid den... Nette Anklage Vatermord Anklage Vatermord Apache Webserver 2.0 Apache Webserver 2.0 Client/Server Survival Guide Client/Ser... Guide Comédia Infantil Comédia Infantil CSS-Praxis CSS-Praxis Dansläraren Återkomst Danslärare... komst Darwin's Radio Darwin's Radio

STORED PROCEDURE AND TRIGGERS

STORED PROCEDURE AND TRIGGERS EGCO321 DATABASE SYSTEMS KANAT POOLSAWASD DEPARTMENT OF COMPUTER ENGINEERING MAHIDOL UNIVERSITY STORED PROCEDURES MySQL is known as the most popular open source RDBMS which