sql行列转换

业务里偶尔会遇到sql行列转换的问题，更多的是面试的时候会遇到...zzz
如下，1.把a表的结果集用sql显示成b表的形式   2.b=>a

select * from table a;
+------+------+---------+
| name | math | english |
+------+------+---------+
| anna |   80 |      97 |
| mike |   76 |      86 |
+------+------+---------+
select * from table b;
+------+---------+-------+
| name | subject | score |
+------+---------+-------+
| anna | shuxue  |    80 |
| anna | yingyu  |    97 |
| mike | shuxue  |    76 |
| mike | yingyu  |    86 |
+------+---------+-------+
--1.a=>b转换
 select name,'shuxue' as subject,math as score from a
 union all
 select name,'yingyu' as subject ,english as score from a
 order by name;
--2.b=>a转换
 select name,max(math) as math,max(english)as english 
 from(
   select name,case when subject='shuxue' then score end as math,
   case when subject='yingyu' then score end as english
   from b ) t 
 group by name;

sql cookbook里有好多例子，一本实用的工具书。