MySQL从两个查询中获取匹配结果？

Question

我有一些PHP代码可以生成多个MySql查询并组合结果。 我试图找到一种方法来组合查询，以便在两个查询中匹配的唯一字段被输出。

PHP代码输出示例。

SELECT LoadData_3 pow FROM tblLoadData WHERE LoadData_1 = 'test1' AND LoadData_2 = 'test2' 
UNION ALL
SELECT LoadData_3 pow FROM tblLoadData WHERE LoadData_1 = 'test3' AND LoadData_2 = 'test4'

我只希望两个查询中的LoadData_3字段相同。

Answer 1

使用INTERSECT操作：

(SELECT LoadData_3 pow 
  FROM tblLoadData 
 WHERE LoadData_1 = 'test1' 
   AND LoadData_2 = 'test2')
INTERSECT                     -- return the intersection of the two queries
(SELECT LoadData_3 pow 
  FROM tblLoadData 
 WHERE LoadData_1 = 'test3' 
   AND LoadData_2 = 'test4')

修改

对于MySQL，您可以使用INNER JOIN USING (..)

SELECT pow -- Use DISTINCT pow instead if you want unique values (like INTERSECT)
  FROM (SELECT LoadData_3 pow 
          FROM tblLoadData 
         WHERE LoadData_1 = 'test1' 
           AND LoadData_2 = 'test2') T1
  INNER JOIN
       (SELECT LoadData_3 pow 
          FROM tblLoadData 
         WHERE LoadData_1 = 'test3' 
           AND LoadData_2 = 'test4') T2
  USING (pow)

或使用WHERE IN子句：

SELECT LoadData_3 pow -- Use DISTINCT pow instead if you want unique values (like INTERSECT)
  FROM tblLoadData 
 WHERE LoadData_1 = 'test1' 
   AND LoadData_2 = 'test2'
   AND LoadData_3 IN (SELECT LoadData_3 pow 
                        FROM tblLoadData 
                       WHERE LoadData_1 = 'test3' 
                         AND LoadData_2 = 'test4')

Answer 2

Big Edit！

我在Oracle上花了太多时间，而且我太快地浏览了那篇文章！上面的答案在我之前编辑过。您还可以查看以下问题：

Alternative to Intersect in MySQL