行转列的问题
查询结果如下:

id   num
01   0
01   1  
01   -1

希望得到如下结果
id   n1   n2   n3
01   0     1     -1


------解决方案--------------------
select a.id from tb a
left join (select * from tb where num = 0) t1 on a.id = t1.id
left join (select * from tb where num = 1) t2 on a.id = t2.id
left join (select * from tb where num = -1) t3 on a.id = t3.id