mysql - 连接两个表（其中一个是另一个的一部分）

Question

我有两个表 Table_A 和 Table_B ，我想加入这些表来选择 Table_c 作为结果：

表_A：

+-----------+-----------+---------+
| tableA_id | tableB_id | v_id    |
+-----------+-----------+---------+
| 1         | 2         | 27      |
| 2         | 3         | 27      |
| 3         | 3         | 28      |
| 4         | 1         | 26      |
| 5         | 2         | 26      |
| 6         | 3         | 26      |
| 7         | 1         | 24      |
| 8         | 1         | 25      |
+-----------+-----------+---------+

表_B：

+-----------+-----------+
| tableB_id | s_name    | 
+-----------+-----------+
| 1         | s1        |
| 2         | s2        | 
| 3         | s3        | 
+-----------+-----------+

表_c：

+-----------+-----------+-----------++--------+
| tableB_id | s_name    | tableA_id | v_id    |
+-----------+-----------+-----------+---------+
| 1         | s1        | null      | null    |
| 2         | s2        | 1         | 27      | 
| 3         | s3        | 2         | 27      |
+-----------+-----------+-----------+---------+

我尝试了不同的查询，但无法达到所需的输出。这是 MYSQL 查询：*编辑：反转表顺序。

SELECT s.tableB_id, s.s_name, v.tableA_id, v.v_id
FROM Table_B  as s 
left OUTER JOIN Table_A  as v
ON v.v_id=27

编辑： 结果应该是左侧的所有 Table_B 数据，并分配给它 table_A 数据（如果有）或使其为空。我怎么能做这个？

最后编辑： 这是我想出的解决方案：

SELECT s.tableB_id , s.s_name, v.tableA_id, v.v_id
FROM Table_B s , Table_A v
WHERE v.v_id=27 AND v.tableB_id = s.tableB_id 

UNION

SeLECT s.tableB_id , s.s_name, null as tableA_id, null as v_id
FROM Table_B s
WHERE s.tableB_id NOT IN (SELECT s.tableB_id 
FROM Table_B s , Table_A v
WHERE v.v_id=27 AND v.tableB_id = s.tableB_id )

Answer 1

你可以试试：

SELECT tb.tableB_id, tb.s_name, ta.tableA_id, ta.v_id
FROM Table_B tb LEFT JOIN Table_A ta
  ON tb.tableB_id = ta.tableB_id

要仅选择一个，您可以使用：

SELECT tb.tableB_id, tb.s_name, ta.tableA_id, ta.v_id
FROM Table_B tb LEFT JOIN 
(SELECT * FROM Table_A 
 WHERE v_id = 27) ta
  ON tb.tableB_id = ta.tableB_id

Answer 2

SELECT distinct s.tableB_id, s.s_name, v.tableA_id, v.v_id
 FROM Table_A as v 
 left OUTER JOIN Table_B as s
 ON v.tableB_id =s.tableB_id and v.v_id = 27;

Answer 3

完全使用这个查询希望你能得到结果

SELECT s.tableB_id, s.s_name, v.tableA_id, v.v_id
FROM Table_A as v 
left OUTER JOIN Table_B as s ON s.tableB_id=v.tableB_id
WHERE v.v_id=27

Answer 4

颠倒顺序，将其b LEFT JOIN a添加到公共列 ( tableB_id) 中：

SELECT s.tableB_id, s.s_name, v.tableA_id, v.v_id
FROM Table_B as s
  LEFT OUTER JOIN Table_A as v 
    ON  v.tableB_id = s.tableB_id
    AND v.v_id=27 ;