mysql> select * from product;
+------------+---------------+
| product_id | name |
+------------+---------------+
| 1 | Car |
| 2 | House |
| 3 | Cat |
| 4 | Blank Product |
+------------+---------------+
4 rows in set (0.00 sec)
mysql> select * from tag;
+--------+-----------+
| tag_id | name |
+--------+-----------+
| 1 | Expensive |
| 2 | Fast |
| 3 | Mean |
| 4 | Large |
| 5 | Small |
| 6 | Alive |
| 7 | Blank Tag |
+--------+-----------+
7 rows in set (0.00 sec)
mysql> select * from product_tag;
+------------+--------+
| product_id | tag_id |
+------------+--------+
| 1 | 1 |
| 1 | 2 |
| 1 | 3 |
| 1 | 4 |
| 2 | 1 |
| 2 | 4 |
| 3 | 2 |
| 3 | 3 |
| 3 | 5 |
| 3 | 6 |
+------------+--------+
10 rows in set (0.00 sec)
다음 쿼리는 내 빈 태그를 반환하지만 내 제품은 반환하지 않는 이유는 무엇입니까?MySQL 다중 오른쪽 조인
mysql> select * from product_tag right join product using (product_id)
right join tag using (tag_id);
+--------+-----------+------------+-------+
| tag_id | name | product_id | name |
+--------+-----------+------------+-------+
| 1 | Expensive | 1 | Car |
| 1 | Expensive | 2 | House |
| 2 | Fast | 1 | Car |
| 2 | Fast | 3 | Cat |
| 3 | Mean | 1 | Car |
| 3 | Mean | 3 | Cat |
| 4 | Large | 1 | Car |
| 4 | Large | 2 | House |
| 5 | Small | 3 | Cat |
| 6 | Alive | 3 | Cat |
| 7 | Blank Tag | NULL | NULL |
+--------+-----------+------------+-------+
11 rows in set (0.00 sec)
태그 7 (빈 태그)을 제품에 연결하는 행이 없지만 나의 오른쪽 조인이이를 리턴합니다. –