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SELECT ename
  ,    job
  ,    CASE deptno
         WHEN 10
           THEN 'ACCOUNTS'
         WHEN 20
           THEN 'SALES'
         ELSE 'UNKNOWN'
       END AS department
FROM emp /* !!! */ 
WHERE department = 'SALES'

这失败了:

ORA-00904:"%s:无效标识符"

有没有办法克服Oracle 10.2 SQL中的这种限制？如何在where子句中使用'case expression column'？