prevent-update-of-column.sql

drop table foo;

create table foo (
  id int unsigned not null auto_increment primary key,
  bar varchar(10) not null
);

insert into foo (bar) values('fluff');

update foo set bar = 'fluff' where id = 1;
update foo set bar = 'bar' where id = 1;


create TRIGGER update_foo before update on foo
  for each row
  begin
    if (NEW.bar != OLD.bar) then signal sqlstate '02123' SET MESSAGE_TEXT = "Cannot update column 'bar' on table 'foo'"; end if;
  end;