MySQL 连接查询 { 如何获取以下结果 }

Question

表1

 +----------+
 |id | data |
 +----------+
 |1  | USRA |
 +----------+
 |4  | USRB |
 +----------+

表2

+----------+
|cid | mid |
+----------+
|1  |  4   |
+----------+
|4  |  1   |
+----------+

结果表

+----------------------+
|table1_id | table2_id |
+----------------------+
|USRA      | USRB      |
+----------------------+
|USRB      | USRA      |
+----------------------+

Answer 1

SELECT
 a.data,
 b.data
FROM
 Table1 a
INNER JOIN
 Table2 t2
ON a.id = t2.cid
INNER JOIN
 Table1 b
ON b.id = t2.mid