One common mistake which is being made on dropping index is that we forget the index name and try to drop the column name.
drop index departments_name_unique on departments;
Incase if you want to join the fields
SELECT DATE, expiry, CONCAT( user.b_fname, " ", user.b_lname ) FROM user
Different types of joins: inner joins, left joins, right joins union/outer joins. This link explains in great detail.
….Sometime simple tip makes someone’s coding life easier…………