Download - Unit6 ProgrammingWithMySQL

Unit 6:Programming with MySQL

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Overview

� Variables

� Flow control constructs

� IF THEN ELSE

� CASE

� LOOP

� WHILE

� REPEAT UNTIL

Basic SQLCopyright © 2010 Pratian Technologies

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� REPEAT UNTIL

� Procedures

� Functions

� Triggers

� Cursors

VARIABLES

� You can store a value in a user-defined variable in onestatement and then refer to it later in another statement

� This enables you to pass values from one statement toanother

� User variables are written as @var_name, where the


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� User variables are written as @var_name, where thevariable name var_name consists of alphanumeric andthe special character “_”

VARIABLES

� Syntax:

� DECLARE @varname1, @varname2, ... data type [DEFAULT

value];

� For Ex:

� DECLARE @Student_Id int;

� DECLARE @Sname, @Cname varchar(15);


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� Variable assignment

� For variable assignments, use either SET or SELECT

� SET @Sname = ‘Krishna’;

� SELECT @Sname := Name FROM Students

WHERE StudentId = 1001;

VARIABLES

� For SET, either = or := can be used as the assignmentoperator.

� For statements other than SET := must be used since =is treated as a comparison operator


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FLOW CONTROL CONSTRUCTS

� Flow Control Constructs include the IF, CASE, LOOP,WHILE, ITERATE, REPEAT and LEAVE constructs

� These constructs can contain single statement or a blockof statements using BEGIN…..END statement.

� These constructs can be nested also.


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� These constructs can be nested also.


� IF Statement

� Syntax

� IF search_condition THEN

statement_list

ELSE IF search_condition THEN

statement_list


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statement_list

ELSE

statement_list

END IF

� For Ex:

� IF @CourseId = 1 THEN

SET @Fees = 1000;


� CASE Statement

� Syntax

� CASE case_value

� WHEN when_value THEN statement_list

� [WHEN when_value THEN statement_list] ... [ELSEstatement_list]

END CASE


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END CASE

Or

CASE

WHEN search_condition THEN statement_list

[WHEN search_condition THEN statement_list] ... [ELSE statement_list]

END CASE


� For Ex:

� DECLARE @shipping_cost INT(2) DEFAULT 0;

� DECLARE @delivery_day INT(2) DEFAULT 0;

� SET @delivery_day := DAYOFWEEK(CURDATE());

CASE @delivery_day


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CASE @delivery_dayWHEN 1 THEN

SET @shipping_cost = 20;WHEN 2 THEN

SET @shipping_cost = 15;WHEN 3 THEN

SET @shipping_cost = 10;ELSE

SET @shipping_cost = 5;END CASE;


� LOOP Statement

� Implements a simple loop construct

� is used to repeat execution of the statement_list,statement_list can contain one or more than one

statements.


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statements.

� Loop is exited with a LEAVE Statement


� Loop Syntax

[begin_label:] LOOP

statement_list

END LOOP [end_label]

� For Ex:� DECLARE @counter INT DEFAULT 0;

simple_loop: LOOP


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simple_loop: LOOP

SET @counter = @counter+1;

SELECT @counter;

IF @counter>=10 THEN

LEAVE simple_loop;

ELSEIF MOD(@counter, 2) = 0 THEN

ITERATE simple_loop;

END IF;

SELECT @counter;

END LOOP simple_loop;


� WHILE Statement

� The WHILE Statement repeats the statement_list until thesearch_condition evaluates to true

� Syntax:

� [begin_label:] WHILE search_condition DO


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� [begin_label:] WHILE search_condition DOstatement_list

END WHILE [end_label]


� For Ex:

� WHILE @count < 10 DO

SET @count = @count + 1;

END WHILE;


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� REPEAT UNTIL Statement

� REPEAT Statement is used to repeat the statement_listuntil the search_condition evaluates to true

� Syntax:

� [begin_label:] REPEAT


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� [begin_label:] REPEATstatement_list

UNTIL search_conditionEND REPEAT [end_label]


� For Ex:

� DECLARE @count INT DEFAULT 0;

increment: REPEATSET @count = @count + 1;SELECT @count;UNTIL @count > 10


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UNTIL @count > 10END REPEAT increment;

PROCEDURES

� Custom programming scripts with embedded SQLstatements that are stored in a compiled form andexecuted directly by the MySQL server

� Allow us to store logic [rules] on the database

� Improves the performance as less information needs to


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� Improves the performance as less information needs tobe sent between the server and the client

� Procedure names can be up to 64 characters long

PROCEDURES

� Advantages of procedures

� Faster Execution: Reduced need for data transfer back and forthbetween a program and the database server.� Note: The use of SPs does not guarantee improved speed as a lot depends

on the code inside of the SP

� Reduced code redundancy: Similar code needed through outthe application can be written once and can be reused. Selects,


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the application can be written once and can be reused. Selects,Inserts, etc..

� Maintenance: If there are changes in the underlying databaseschema, code changes can be localized to a few SPs

� Security: Direct access to tables by user programs is a problemand with SPs, data access can be monitored, and logged ifnecessary. Centralized security rules can be applied

PROCEDURES

� Syntax:

� CREATE PROCEDURE proc_name [proc_parameter[......]]) routine_body

� proc_name : procedure nameproc_parameter : [ IN | OUT | INOUT ] param_name typeroutine_body : Valid SQL procedure statement


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routine_body : Valid SQL procedure statement

PROCEDURES

� If you don't specify IN, OUT, or INOUT for the parameter,it will default to IN

� An IN parameter is passed into the stored procedure touse internally

� An OUT parameter is set within the procedure, butaccessed by the caller

� An INOUT parameter is passed into the procedure for


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� An INOUT parameter is passed into the procedure forinternal use, but is also available to the caller after theprocedure has completed

� The name and data type of the parameter are used in thestored procedure for referencing and setting values goingin and out of the procedure

� The data type can be any valid data type for

MySQL

PROCEDURES

� For Ex:

� Without parameters

� CREATE PROCEDURE GetStudents()

BEGIN

SELECT * FROM Students

END


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� With IN Parameter

� CREATE PROCEDURE GetFeesForStudent(@StudentId INT)

BEGIN

SELECT Fees

FROM Students

WHERE StudentId = @StudentId

END

PROCEDURES

� With IN and OUT parameters

� CREATE PROCEDURE GetFeesForStudent(@StudentId INT,OUT @TotalFees INT)

BEGIN

SELECT @TotalFees := Fees

FROM Students

WHERE StudentId = @StudentId

END


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END

� Method to invoke a procedure

� CALL GetStudents();

� CALL GetFeesForStudent(1001);

� CALL GetFeesForStudent(1001, @TotalFees);

PROCEDURES

� ALTER PROCEDURE

� A procedure can be altered once created

� Syntax:

� ALTER PROCEDURE proc_name [proc_parameter[......]]) routine_body

� proc_name : procedure name


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� proc_name : procedure nameproc_parameter : [ IN | OUT | INOUT ] param_name typeroutine_body : Valid SQL procedure statement

� DROP PROCDURE

� DROP PROCEDURE IF EXISTS procedure_name

FUNCTIONS

� Functions are also scripts with embedded SQLstatements, that are stored in a compiled form andexecuted directly by MySQL server

� The main differences between a function and a procedureare

� Function can return only one value and procedure can return one


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� Function can return only one value and procedure can return oneor more values

� Functions don’t have different set of parameters like procedures.Parameters can only be supplied to Functions

� Functions may internally invoke other functions only unlikeprocedures which can invoke other procedures or functions

FUNCTIONS

� Syntax:

� CREATE FUNCTION func_name ([func_parameter[,...]])RETURNS type

routine_body

� func_name : Function namefunc_parameter : param_name typetype : Any valid MySQL datatype


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type : Any valid MySQL datatyperoutine_body : Valid SQL procedure statement

� The RETURN clause is mandatory for FUNCTION

� Method to invoke a function

� Function_name();

FUNCTIONS

� For Ex:

� CREATE FUNCTION reduce(str VARCHAR(255), len INT)RETURNS VARCHAR(255)

� BEGIN

� IF ISNULL(str) THEN

� RETURN NULL;

� END IF;

� IF len = 0 OR CHAR_LENGTH( str ) = 0 OR CHAR_LENGTH(


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� IF len = 0 OR CHAR_LENGTH( str ) = 0 OR CHAR_LENGTH(str ) <= len THEN

� RETURN str;

� ELSE

� RETURN CONCAT( LEFT( str, len - 10 ), ' ___ ', RIGHT(str, 5 ) );

� END IF;

� END

FUNCTIONS

� ALTER FUNCTION

� ALTER FUNCTION func_name ([func_parameter[,...]])RETURNS type

routine_body

� func_name : Function namefunc_parameter : param_name typetype : Any valid MySQL datatype


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type : Any valid MySQL datatyperoutine_body : Valid SQL statements

� DROP FUNCTION

� DROP FUNCTION IF EXISTS function_name;

TRIGGERS

� A named database object which defines some action thatthe database should take when some databases relatedevent occurs

� Are automatic execution of SQL commands or a storedprocedure after or before INSERT, UPDATE,

or DELETE commands


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or DELETE commands

TRIGGERS

� Syntax:

� CREATE TRIGGER trigger_name trigger_time trigger_event ONtbl_name FOR EACH ROW trigger_statement

� Trigger_time means trigger action time

� Trigger_event specifies the statement that executes the trigger


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� Trigger_statement has the statement that executes when thetrigger fires but if you want to execute multiple statements thenyou have to use the BEGIN…END compound statement.

TRIGGERS

� For Ex: [To insert default CourseId after student insert.

� CREATE TRIGGER ins_trig AFTER INSERT ON Students

FOR EACH ROW

BEGIN

INSERT INTO StudentCourses (StudentId, CourseId) VALUES(NEW.StudentId, 1)

END;


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� INSERT INTO Students (StudentId, Name, Fees, JoinDate)

VALUES (1004, ‘Krishna Kumar S’, 1000, ‘2010-12-05’)

TRIGGERS

� For Ex:

� CREATE TRIGGER updtrigger BEFORE UPDATE ON Students FOR EACH ROW

BEGIN

IF NEW.Fees <= 1000 THEN

SET NEW.Fees =1000;


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END IF;

END

� UPDATE Students SET Fees = 500 WHERE StudentId = 1001;

TRIGGERS

� Note:

� There cannot be two triggers at the same time for the same actionon a table

� Up to six triggers can be defined for each table

� Every trigger name has to be unique

� OLD.column_name is used to refer the column of an existing rowbefore it is deleted or updated

� NEW.column_name is used to refer the column of a new row that


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� NEW.column_name is used to refer the column of a new row thatis inserted or after updated existing row

� To delete a trigger

� DROP TRIGGER updtrigger;

CURSORS

� Cursors are used when the SQL Select statement isexpected to return more than one row

� Cursors are supported inside procedures and functions

� Cursors must be declared and its definition contains thequery


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query

� A cursor must be opened before processing, data shouldbe fetched for processing and closed after processing

CURSORS

� Syntax:

� DECLARE <cursor_name> CURSOR FOR <select_statement>

� OPEN <cursor_name>

� FETCH <cursor_name> INTO <var1>,<var2>……


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� FETCH <cursor_name> INTO <var1>,<var2>……

� CLOSE <cursor_name>

CURSORS

� For EX:

� DECLARE @StudentId, @record_not_found int DEFAULT 0;

� DECLARE @StudentCursor CURSOR FOR

� SELECT StudentId From Students

� DECLARE CONTINUE HANDLER FOR NOT FOUND

SET @record_not_found = 1

� OPEN CURSOR @StudentCursor


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� Cursorloop: LOOP

� IF @record_not_found THEN� LEAVE Cursorloop;

� FETCH @StudentCursor INTO @StudentId

� INSERT INTO StudentCourses (StudentId, CourseId)

VALUES (@StudentId, 1);

� END LOOP Cursorloop

� CLOSE @StudentCursor

Please try to limit the questions to the topics discussed during the session. Thank you

.

Question Time


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