> I would do a CHECK (trim(a) <> '')
TRIM() would add some processing time, so I'd include it only if there
was a chance of spaces getting added. From a puritanical point of
view, it is definitely a good idea.
To the original poster, this syntax should work in MySQL as well:
create table mytable (mycol text not null check (mycol <> ''));
Problem is, if you created your table before MySQL 5, and now simply
want to ALTER your table (which is what I gather you wish to do, as
you already have the table) then adding the CHECK condition may not
work.
I cannot help in this case, and from the turn this thread has taken,
not many others I suppose. Why not try a MySQL experts list instead of
PostgreSQL, but be prepared to have to recreate the table in MySQL 5
with the CHECK constraint, and then importing your data in to it.
Good luck!