Il existe un moyen d'utiliser un champ calculé dans la clause where?

Question

Il existe un moyen d'utiliser un champ calculé dans la clause where?

Je veux faire quelque chose comme

SELECT a, b, a+b as TOTAL FROM (
    select 7 as a, 8 as b FROM DUAL 
    UNION ALL 
    select 8 as a, 8 as b FROM DUAL 
    UNION ALL 
    select 0 as a, 0 as b FROM DUAL 
) 
WHERE TOTAL <> 0 
; 

mais je reçois ORA-00904: "TOTAL": identificateur non valide.

donc je dois utiliser

SELECT a, b, a+b as TOTAL FROM (
    select 7 as a, 8 as b FROM DUAL 
    UNION ALL 
    select 8 as a, 8 as b FROM DUAL 
    UNION ALL 
    select 0 as a, 0 as b FROM DUAL 
) 
WHERE a+b <> 0 
; 

Answer 1

Logiquement, la clause select est l'une des dernières parties d'une requête évaluée, de sorte que les alias et les colonnes dérivées ne sont pas disponibles. (. Sauf order by, qui logiquement arrive dernier)

En utilisant une table dérivée se trouve autour de cette:

select * 
from (SELECT a, b, a+b as TOTAL FROM ( 
      select 7 as a, 8 as b FROM DUAL 
      UNION ALL 
      select 8 as a, 8 as b FROM DUAL 
      UNION ALL 
      select 0 as a, 0 as b FROM DUAL) 
    ) 
WHERE TOTAL <> 0 
;