C'è un modo per usare un campo calcolato nella clausola where?

Question

Esiste un modo per utilizzare un campo calcolato nella clausola where?

voglio fare qualcosa di simile

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 
; 

ma ottengo ORA-00904: "TOTALE": identificatore non valido.

quindi devo usare

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

Logicamente, la clausola select è una delle ultime parti di una query valutati, così gli alias e le colonne derivate non sono disponibili. (. Tranne per order by, che logicamente accade scorso)

Utilizzando una tabella derivata è lontano intorno a questo:

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 
;