Question

x_Id  | y_Id | z_Id
----- |----- |-----
1     | 1    | 1
2     | 1    | 1
3     | 1    | 1
4     | 1    | 1
5     | 1    | 1
1     | 2    | 3

我在编程方面相对较新，我无法弄清楚这个MySql查询。我只需要选择x_Id（（y_Id = 1 AND z_Id = 1）AND（y_Id = 2 AND z_Id = 3））。因此，使用这些数字作为示例，唯一应该选择的是（x_Id =）1。

**所有这些列都在同一个表中

我最接近的是使用此查询：

SELECT 
    * 
FROM 
    `relationships` 
WHERE
    y_id = 1 AND
    z_id = 1

UNION    
SELECT 
    * 
FROM 
    `relationships` 
WHERE
    z_id = 3 AND
    y_id = 2

但是，这将再次返回所有x_ids和x_id = 1。

**我正在使用sqlPro和MySql 5

Answer 1

无需联盟。

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select
*
from relationships T1
INNER JOIN relationshipsT2 on t1.x_Id   = t2.x_Id  where
((T1.y_Id = 1 AND T1.z_Id = 1) AND (T2.y_Id  = 2 AND T2.zz_Id= 3))

您也只能返回x_Id而不是*

Answer 2

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使用汇总SUM()，您可以累计每个值x_id达到的条件数。如果总数> 1，这两个条件都在表中的某个地方得到满足。

SELECT DISTINCT x_id FROM (
  SELECT
    x_id,
    SUMCASE WHEN (y_id = 1 AND z_id = 1) OR (z_id = 3 AND y_id = 2) THEN 1 ELSE 0 END) AS hasboth
  FROM relationships
  GROUP BY x_id
  HAVING hasboth > 1
) subq

Answer 3

如果您只对x_id值感兴趣，可以使用上面的查询，但只需添加DISTINCT并仅投影x_id值。

示例：

SELECT 
    DISTINCT x_id 
FROM 
 `relationships` 
WHERE
     y_id = 1 AND z_id = 1

UNION

SELECT 
    DISTINCT x_id 
FROM 
    `relationships` 
WHERE
    z_id = 3 AND y_id = 2

除了WHERE子句中使用OR之外，还有其他一些方法可以做到更简单。

MySQL 3列查询返回重复项

3 个答案:

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