Mysql select column only if a condition

Question

I have a simple query

SELECT 
   gruppo.*, comuni.Nome as nomecomune 
FROM 
   gruppo, comuni 
WHERE 
   (comuni.ID_Comuni = gruppo.ID_Comuni or gruppo.ID_Comuni ='0') 
   AND ID_Gruppo='3'

How you can understand from where cause I need to always show a row where ID_Gruppo='3' , but if gruppo.ID_Comuni='0' (so if there is not a link) I need to don't SELECT comuni.Nome column.

The above query works, but if there is not a link between tables ( gruppo.ID_Comuni=0 ) show anyway a (random?) comuni.Nome value.

So, I need to do something like this:

SELECT 
   gruppo.*,` 
   if(gruppo.ID_Comuni <> '0') then also select `comuni.Nome 
FROM
   gruppo, comuni 
WHERE
   (comuni.ID_Comuni = gruppo.ID_Comuni OR gruppo.ID_Comuni = '0') AND ID_Gruppo = '3'

I hope I have been clear, thank you for your help.

Answer 1

It is not possible, to write an SELECT column ONLY IF... FROM ..

You are also don't getting random results - you query is performing some kind of cross-join, where it joins each row from the table comuni to each row from table gruppo , where gruppo.ID_Comuni = 0 .

If you need a "select only if.."-command, you have to write a stored procedure, or an sql-script.