MySQL链接表获取与table.value分手的最后一行= X

Question

我当前有一个表项目（ID）和一个表project_step（ID，项目，步骤（整数））。

1个项目链接到1个或多个project_step。

我想要得到的项目中最后一个进入project_step（project_step.id DESC）具有阶梯= X.

我需要这样做在子查询的列表，但我不知道如何写下来。

Answer 1

该查询将返回两个表中的所有列。额外子查询的目的是分别获得表project_step上每project的最新ID。

SELECT a.*, b.* 
FROM project a 
     INNER JOIN project_step b 
      ON a.ID = b.project 
     INNER JOIN 
     (
      SELECT project, MAX(ID) ID 
      FROM project_step 
      GROUP BY project 
     ) c ON b.project = c.project AND 
       b.ID = c.ID 
WHERE b.step = ? 

Answer 2

尝试类似这样的东西。

SELECT project.* from project_step 
JOIN project ON project.id = project_step.project 
GROUP BY project 
HAVING SUBSTRING_INDEX(GROUP_CONCAT(step ORDER BY step DESC SEPARATOR ' '), ' ', 1) = X