Question

I have the following three (InnoDB-) tables in a MySQL database:

Entity (DLID)
Category (CatID, CatName)
hasCategory (DLID, CatID)

Now, upon insertion into the table hasCategory I would like to make sure, that each Entity is associated with at least one Category. Thus, I wrote the following trigger:

delimiter |

create trigger Max before insert on hasCategory for each row begin
    if  (exists (select distinct DLID from Entity where not exists (select distinct new.DLID from new))) then
        signal sqlstate '45000'
            set message_text = 'Min of 1 category per entity required';
    end if;
end|

delimiter ;

Now, when I execute the following query: insert into hasCategory values (1, 1); I get the error error code 1146: table mydb.new does not exist. I have created some other triggers similar to this one, also referring to the new-table, where it worked perfectly well. Yet, I don’t get it, what causes the error in this particular trigger.

Is it possible that the select statement causes some trouble? I’ve read that only select into statements are valid in procedures, but I don’t know if this has got anything to do with this.

Thanks for your help!

Answer 1

select distinct new.DLID from new

there is no table new in your DB just as the error states. You can use NEW for the record that will be inserted in your trigger but you cannot use it as a table name and select from it.

try

if (select 1 from Entity where DLID = new.DLID) = 1 then