在MySQL中将多行转换为列

Question

我有两张桌子:

表A

+-------+--------+
| Data  | Acc_No |
+-------+--------+
| Unix  |     10 |
| Linux |     20 |
+-------+--------+ 

表B

+-----+----------+--------+
| Obj | Type     | Amount |
+-----+----------+--------+
|  10 | rev      | 100.00 |
|  10 | revision | 200.00 |
+-----+----------+--------+

我希望输出像这样

 +-------+--------+----------+--------+-----------+----------+
 | Data  | Acc_No | Type     | Amount | Type_1    | Amount_1 |
 +-------+--------+----------+--------+-----------+----------+
 | Unix  | 10     | rev      | 100    | revision  | 200      |
 +-------+--------+----------+--------+-----------+----------+

我尝试使用简单的连接.这是查询:

SELECT a.Data,a.Acc_No, b.Type, b.Amount, bb.Type AS "Type_1", bb.Amount AS "Amount_1"
FROM TableA a,TableB b, TableB bb
WHERE a.Acc_No = b.Obj AND
      b.Obj = bb.Obj AND
      bb.Obj = a.Acc_No AND
      a.Acc_No =10;

但我得到了这个输出.

+------+--------+----------+--------+----------+----------+
| Data | Acc_No | Type     | Amount | Type_1   | Amount_1 |
+------+--------+----------+--------+----------+----------+
| Unix |     10 | rev      | 100.00 | rev      |   100.00 |
| Unix |     10 | revision | 200.00 | rev      |   100.00 |
| Unix |     10 | rev      | 100.00 | revision |   200.00 |
| Unix |     10 | revision | 200.00 | revision |   200.00 |
+------+--------+----------+--------+----------+----------+

我试着在这个网站上搜索答案,我甚至用Google搜索,但我找不到合适的答案.

Answer 1

您当前的查询已关闭,但我建议对其进行一些小的更改以获得结果.如果要使用JOIN"旋转"数据,则需要区分要TableB在每个后续连接中返回的值.

例如,当您想要返回时type=rev,您需要为该值包含特定的过滤器.然后你会做同样的事情type=revision.我还建议使用a LEFT JOIN加入,TableB如果你没有两个type值,Acc_no那么你仍然会返回数据.

select
  a.data,
  a.acc_no,
  b.type,
  b.amount,
  bb.type as type_1,
  bb.amount as amount_1
from tablea a
left join tableb b
  on a.acc_no = b.obj
  and b.type = 'rev'
left join tableb bb
  on a.acc_no = bb.obj
  and bb.type = 'revision';

请参阅SQL Fiddle with Demo

您也可以使用某些条件聚合获得此结果,然后您不必TableB多次加入:

select
  a.data,
  a.acc_no,
  max(case when b.type = 'rev' then b.type end) as type,
  max(case when b.type = 'rev' then b.Amount end) as Amount,
  max(case when b.type = 'revision' then b.type end) as type_1,
  max(case when b.type = 'revision' then b.Amount end) as Amount_1
from tablea a
left join tableb b
  on a.acc_no = b.obj
group by a.data, a.acc_no
order by a.acc_no;

请参阅SQL Fiddle with Demo