use test;      
drop table if exists rooms, area;
create table rooms ( width double(5,2) default 0, length double(5,2) default 0, location int );
insert into rooms values ( 12.0 ,6.0, 1), (15.0, 4.0, 1), (18.0, 4.0, 3), (4.0, 4.0, 2);
select @area := length * width from rooms;
create table area ( area double(5,2));
insert into area select @area := length * width from rooms;
select * from area;
select distinct( area ) from area;
truncate area;
insert into area select distinct @area := length * width from rooms;
select * from area;