有 两种case表达式.您可以使用许多 WHEN 作为 CASE 作为;

There are two formats of case expression. You can do CASE with many WHEN as;

CASE  WHEN Col1 = 1 OR Col3 = 1  THEN 1 
      WHEN Col1 = 2 THEN 2
      ...
      ELSE 0 END as Qty

或一个简单的CASE表达式

CASE Col1 WHEN 1 THEN 11 WHEN 2 THEN 21 ELSE 13 END

或 CASE 内 CASE as;

CASE  WHEN Col1 < 2 THEN  
                    CASE Col2 WHEN 'X' THEN 10 ELSE 11 END
      WHEN Col1 = 2 THEN 2
      ...
      ELSE 0 END as Qty