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Como usar Alias ​​na cláusula Where?


Você não pode fazer referência ao alias da coluna na cláusula WHERE - suas opções são:
  • replicar a instrução CASE na cláusula WHERE

  • use uma subconsulta:
    PROCEDURE P_LOAD_EXPIRED_ACCOUNT(pDayDiff NUMBER,
                                 ExpiredCur OUT MEGAGREEN_CUR)
IS
BEGIN


   OPEN ExpiredCur FOR
   SELECT x.account_name,
          x.service_type, 
          x.expired_date
     FROM (SELECT s.account_name,
                  s.service_type, 
                  CASE 
                     WHEN s.service_type = 1 THEN ADD_MONTHS(ACTIVATED_DATE,3)
                     WHEN s.service_type = 2 THEN ADD_MONTHS(ACTIVATED_DATE,6)
                     WHEN s.service_type = 3 THEN ADD_MONTHS(ACTIVATED_DATE,12)        
                  END AS EXPIRED_DATE
             FROM SUBSCRIBERS s) x
    WHERE x.expired_date - CURRENT_DATE < pDayDiff;


END;

    Oracle 9i+

    WITH summary AS (
  SELECT s.account_name,
         s.service_type, 
         CASE 
            WHEN s.service_type = 1 THEN ADD_MONTHS(ACTIVATED_DATE,3)
            WHEN s.service_type = 2 THEN ADD_MONTHS(ACTIVATED_DATE,6)
            WHEN s.service_type = 3 THEN ADD_MONTHS(ACTIVATED_DATE,12)        
         END AS EXPIRED_DATE
    FROM SUBSCRIBERS s)
   SELECT x.account_name,
          x.service_type, 
          x.expired_date
     FROM summary x
    WHERE x.expired_date - CURRENT_DATE < pDayDiff;