# `OUTER JOIN` 和 `NULL` 
+ `NULL` 在外联中的行为:

__*NULL 的行为*__

```
tidb> select a.name, d.name from test.a a right join test.d d on a.id=d.id;
+------+------+
| name | name |
+------+------+
| AA   | DA   |
| AB   | DB   |
| NULL | DC   |
| NULL | NULL |
+------+------+
tidb> select a.name, d.name, a.id, d.id from test.a a right join test.d d on a.id=d.id;
+------+------+------+------+
| name | name | id   | id   |
+------+------+------+------+
| AA   | DA   |    1 |    1 |
| AB   | DB   |    2 |    2 |
| NULL | DC   | NULL | NULL |
| NULL | NULL | NULL |    ~!@5@!~ |
+------+------+------+------+
```
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