php - 搜索多行mysql

Question

我有两个表 projects 和 projects_meta

   Projects
    --------------------
    id  name
    --------------------
    1   A    
    2   B
    3   C

projects_meta
------------------------------------------------------------
id    project_id   additional_field  additional_value
------------------------------------------------------------
1     1            verified_by       Erik
2     1            approved_by       Dave
3     2            verified_by       Riyaj
4     2            approved_by       Mike
5     3            verified_by       Erik
6     3            approved_by       Dave

现在我想要连接两个表的输出，以找出由 Erik 验证并由 Dave 批准的项目

SELECT * 
FROM projects a 
INNER JOIN projects_meta b 
ON a.id = b.project_id 
WHERE b.additional_field= 'verified_by' 
AND b.additional_value = 'Erik' 
AND b.additional_field= 'approved_by' 
AND b.additional_value = 'Dave'

上面的查询似乎适用于单个条件，但当有更多条件时，它返回空结果。

提前致谢

Answer 1

您需要 JOIN 两次到 projects_meta 表:

SELECT * 
FROM projects a 
INNER JOIN projects_meta b ON a.id = b.project_id 
INNER JOIN projects_meta c ON a.id = c.project_id 
WHERE b.additional_field= 'verified_by' AND b.additional_value = 'Erik' AND 
      c.additional_field= 'approved_by' AND c.additional_value = 'Dave'

上述查询返回所有链接到“verified_by Erik” 和“approved_by Dave” 记录的项目。