in this code-
CREATE TABLE `tablename` ( `id` int(10) unsigned NOT NULL auto_increment, `a` varchar(10) NOT NULL, `b` varchar(45) default NULL, `c` varchar(45) NOT NULL, `d` varchar(45) default NULL, PRIMARY KEY (`id`), KEY `Index_a` (`a`), KEY `Index_bcd` (`b`,`c`,`d`), KEY `Index_cd` (`c`,`d`) ) ....;
what do the lines that start with KEY?
I know PRIMARY KEY sets the pk of the table.. but I don't understand the rest of the lines..
does that have to do something with setting indexes to make searches faster? or something like that?