oracle decode 函数

DECODE 

语法: 

SELECT DECODE( <EXPR,SEARCH1,RESULT1,SEARCH2,RESULT2,...[,DEFAULT]>)
FROM <TABLE_NAME>

e.g.:

select orderno,decode(ostatus,'p','准备处理','c','已完成') 

from order_master

此函数可用于行转列:

select * from score

SELECT   u_id, stu_name, 
         SUM (DECODE (score_type, '语文', score, 0)) AS 语文, /*or use max()*/
         SUM (DECODE (score_type, '数学', score, 0)) AS 数学,
         SUM (DECODE (score_type, '外语', score, 0)) AS 外语
    FROM score
--where u_id>1
GROUP BY u_id, stu_name
--having u_id >1
ORDER BY u_id