如题, 下面是我的试验结果
左表
select buildingNumCode,estateId from sell;
+-----------------+----------+
| buildingNumCode | estateId |
+-----------------+----------+
| NULL | 12 |
| 0 | 11 |
+-----------------+----------+
右表
select buildingNumCode,estateId from estate_building;
+-----------------+----------+
| buildingNumCode | estateId |
+-----------------+----------+
| 0 | 1 |
| 1 | 1 |
| 0 | 2 |
| 0 | 11 |
| 0 | 12 |
| 0 | 10 |
| 0 | 11 |
+-----------------+----------+
连接后
select a.estateid,a.buildingNumCode from sell a
left join estate_building b on (a.buildingNumCode=b.buildingNumCode and a.estateId=b.estateId);
+----------+-----------------+
| estateid | buildingNumCode |
+----------+-----------------+
| 12 | NULL |
| 11 | 0 |
| 11 | 0 |
+----------+-----------------+
左表
select buildingNumCode,estateId from sell;
+-----------------+----------+
| buildingNumCode | estateId |
+-----------------+----------+
| NULL | 12 |
| 0 | 11 |
+-----------------+----------+
右表
select buildingNumCode,estateId from estate_building;
+-----------------+----------+
| buildingNumCode | estateId |
+-----------------+----------+
| 0 | 1 |
| 1 | 1 |
| 0 | 2 |
| 0 | 11 |
| 0 | 12 |
| 0 | 10 |
| 0 | 11 |
+-----------------+----------+
连接后
select a.estateid,a.buildingNumCode from sell a
left join estate_building b on (a.buildingNumCode=b.buildingNumCode and a.estateId=b.estateId);
+----------+-----------------+
| estateid | buildingNumCode |
+----------+-----------------+
| 12 | NULL |
| 11 | 0 |
| 11 | 0 |
+----------+-----------------+
+-----------------+----------+
| buildingNumCode | estateId |
+-----------------+----------+
| 0 | 1 |
| 1 | 1 |
| 0 | 2 |
| 0 | 11 |
| 0 | 12 |
| 0 | 10 |
| 0 | 11 |
+-----------------+----------+
这张表中本身就有两条。
这张表中本身就有两条。可是它是右表啊,难道我理解错了?