MySQL Database Object Existance Check SQL Example

database object existance check by optimize sql example in a single mysql/mssql/oracle query

check an object in database is exist or not example

user table structure

    `USER_ID` int(10) NOT NULL auto_increment,             
    `USER` varchar(255) default NULL,                      
    `EMAIL` varchar(255) default NULL,                     
    `PASSWORD` varchar(20) default NULL,                   
    `USER_TYPE_ID` int(10) NOT NULL,                       
    `STATUS` int(1) default '1',                           
    `PUBLISH` int(1) default '0',                          
    `DATE_CREATED` datetime default NULL,                  
    `DATE_UPDATED` datetime default NULL,                  
    PRIMARY KEY  (`USER_ID`)                               

Insert some sample data then try to retrive as follows by using PHP

        | CASE :
        | a new user want to register in your database.
        | you need to check whether a user holding the
        | information is already exist or not.
        $sql = " SELECT * FROM user WHERE EMAIL = 'www@www.www' AND PASSWORD = 'password' ";
        | this query works fine but use more resource.
        | let's optimize it.
        $sql = " SELECT EMAIL FROM user WHERE EMAIL = 'www@www.www' AND PASSWORD = 'password' ";
        | still it can be optimized for better performance
        $sql = " SELECT 'nothing' FROM user WHERE EMAIL = 'www@www.www' AND PASSWORD = 'password' ";
        | this time db server doesnt select anything but
        | a string and better performance is obtained.

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