Re: How to Raise Error ?

[Zigmund Bulinsh]

To raise error in transaction or trigger the best way is to use not existable procedure. For example:

delimiter |
create trigger settings_before_insert before insert on _settings
for each row
begin
if (select ifnull(count(*),0) from _settings)=1 then
call ERROR_INSERT_NOT_ALLOWED();
end if;
end;
| delimiter;

And then in Delphi (of course) you simply can intercept this exception and show your message instead of this. Of course procedure ERROR_INSERT_NOT_ALLOWED must not exist.
I saw stupid decision of this problem with using a table with unique index on some field and insert then two same records - don't use this stupid method, my method is better.