sql - Add Index to Existing MySQL Table -

i have database in tables in use no index defined. i'm looking increase speed if possible. have ready on indexes, wondering need primary key well? also, index null old records in table. issue? i'm wondering best approach is.

here current table stucture (i planning on inserting 'id' index)

field   type    collation   attributes  null user    varchar(255)    utf8_general_ci     no pass    varchar(255)    utf8_general_ci     no ts  varchar(255)    utf8_general_ci     no lat varchar(255)    utf8_general_ci         no 

try this:-

create fulltext index `idxtags` on `table1`(`tags`) 

and if want can try also:-

alter table tablename add id int not null auto_increment primary key; 

this add unique index on rows.