在这种情况下，如何从多个 mysql 表中选择数据?

问题描述：

好吧，我有一个奇怪的场景，我无法更改数据库结构，因为我没有权限.对于这个问题，我有三个表

Ok I have a bit of a weird scenario, and I can't change the database structure, because I don't have the permission for that. For the problem, i have three tables

表 1-

  id(int) | name(varchar) | link_id(int) | link_to(tinyint)
..............................................................
    1       | value1        | 1            | 2
    2       | value2        | 3            | 2
    3       | value3        | 1            | 3
    4       | value4        | 2            | 3
    5       | value5        | 3            | 3

表 2-

  id(int)  | data(varchar)
............................
    1       | some1       
    2       | some2       
    3       | some3

表 3-

    id(int) | data(varchar)
............................
    1       | another1       
    2       | another2       
    3       | another3

现在让我解释一下:在 table 1 中，link_id 是 table 2 或table 3 和 link_to 说明它是链接到表 2 还是表 3.

Now let me explain: in table 1, link_id is the id field of either table 2 or table 3, and link_to states whether it is linked to table 2 or 3.

现在我需要从所有 3 个表中获取组合数据，以便针对 table 1 中的每个 name 字段，我得到 data 正确表中的字段，由该行中的 link_id 和 link_to 字段定义.

Now I need to fetch the combined data from all 3 tables such that, against each name field in table 1, I get the data field from the correct table as defined by the link_id and link_to fields in that row.

是否有任何 mysql 查询可以实现此目的?

Is there any mysql query for achieving this?

答

您可以尝试使用 UNION

You could try with a UNION

(
SELECT t1.id,t2.data
FROM table1 t1
    INNER JOIN table2 t2 ON t1.link_id=t2.id AND t1.link_to=2
) UNION (
SELECT t1.id,t3.data
FROM table1 t1
    INNER JOIN table3 t3 ON t1.link_id=t3.id AND t1.link_to=3
)

在这种情况下，如何从多个 mysql 表中选择数据?

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