有没有办法从这样的表中获取mysql结果？

Question

我有一张桌子＆＃34;提供＆＃34;如下，

pid | sellerid | offer
1   |    1     |  30
1   |    2     |  32
1   |    3     |  31
2   |    2     |  60
3   |    3     |  45

我想要结果如下，

pid | seller1price | seller2price | seller3price
1   |      30      |      32      |     31
2   |      --      |      60      |     --
3   |      --      |      --      |     45

如果未找到记录，则可以将其替换为0或仅 - 。我尝试了跟随和许多其他方法，但没有得到空值

  select a.pid as pid, a.offer as seller1price, b.offer as seller2price, c.offer as seller3price from offers as a,  offers as b,  offers as c where a.pid=b.pid and b.pid=c.pid group by a.pid;

但是这会跳过空记录而只获得第一条记录。我试过加入但也失败了。

任何帮助都可以被欣赏。