Case语句使用技巧

示例一

SELECT  学号, 姓名, 
 等级 =  
     CASE  
     WHEN  总学分  IS   NULL   THEN  ‘尚未选课’
        WHEN  总学分  <   50   THEN  ‘不及格’
         WHEN  总学分  >= 50   and  总学分 <= 52   THEN  ‘合格’
         ELSE  ‘优秀’
     END    FROM   XS     WHERE  专业名 = ’计算机’

示例二示例三

select a, (case a when 1 then '中' else '国' end) AS B  from table1

示例四

USE  pubs 
GO  
SELECT  
     CASE  
         WHEN  price  IS   NULL   THEN   ' Unpriced '  
         WHEN  price  <   10   THEN   ' Bargain '  
         WHEN  price  BETWEEN   10   and   20   THEN   ' Average '  
         ELSE   ' Gift to impress relatives '  
     END   AS  Range, 
    Title 
FROM  titles 
GROUP   BY  
     CASE  
         WHEN  price  IS   NULL   THEN   ' Unpriced '  
         WHEN  price  <   10   THEN   ' Bargain '  
         WHEN  price  BETWEEN   10   and   20   THEN   ' Average '  
         ELSE   ' Gift to impress relatives '  
     END , 
    Title 
ORDER   BY  
     CASE  
         WHEN  price  IS   NULL   THEN   ' Unpriced '  
         WHEN  price  <   10   THEN   ' Bargain '  
         WHEN  price  BETWEEN   10   and   20   THEN   ' Average '  
         ELSE   ' Gift to impress relatives '  
     END , 
    Title 
GO