Suppose table:


CREATE TABLE `testtable` (
`id` INT NOT NULL AUTO_INCREMENT PRIMARY KEY ,
`fieldA` INT NOT NULL ,
`fieldB` INT NOT NULL ,
`fieldC` INT NOT NULL ,
`fieldD` INT NOT NULL
) ENGINE = MYISAM ;

What's the diffrence between:
ALTER TABLE `testtable` ADD INDEX ( `fieldA` )
ALTER TABLE `testtable` ADD INDEX ( `fieldB` )
ALTER TABLE `testtable` ADD INDEX ( `fieldC` )

....And:
ALTER TABLE `testtable` ADD INDEX ( `fieldA` , `fieldB` , `fieldC` ) ;


Take care,
Quarco