多个内连接和子查询的查询优化

Question

我需要有关以下查询的查询优化方面的帮助。

SELECT pr.todate , pr.descr, cmp.company_id 
FROM employee AS emp
INNER JOIN company AS cmp ON emp.emp_comp_id = cmp.company_id 
INNER JOIN profile AS pr ON emp.acca_id = pr.profile_id 
INNER JOIN acondition ON as_id = as_ac_id
WHERE as_closed = 0 
  AND (pr.ac_act_id = 20)
  AND (pr.todate = (SELECT MIN(todate) AS Expr1 
                    FROM profile pro 
                    INNER JOIN employee empl ON empl.acca_id = pro.profile_id 
                    JOIN acondition ON as_id = as_ac_id 
                    WHERE (pro.ac_act_id = 20 
                           AND empl.emp_comp_id = cmp.company_id) 
                      AND as_closed = 0)) 

由于主查询和子查询有重复的join，有什么办法可以去掉子查询中的join？

Answer 1

因为，正如您所澄清的，您的子查询几乎与您的主查询相同，您可以使用窗口函数 RANK 作为过滤条件。 RANK 为关系分配相同的编号，这意味着如果每个公司的多个记录匹配，您将获得所有记录，例如

SELECT todate, descr, company_id
FROM (
    SELECT pr.todate, pr.descr, cmp.company_id
      , RANK() OVER (PARTITION BY cmp.company_id ORDER BY pr.todate ASC) RankNumber
    FROM employee AS emp
    INNER JOIN company AS cmp ON emp.emp_comp_id = cmp.company_id 
    INNER JOIN profile AS pr ON emp.acca_id = pr.profile_id 
    INNER JOIN acondition ON as_id = as_ac_id
    WHERE as_closed = 0 AND pr.ac_act_id = 20
) X
where RankNumber = 1;

Answer 2

这对你有用吗？

SELECT ca.todate , pr.descr, cmp.company_id 
FROM employee AS emp
INNER JOIN company AS cmp ON emp.emp_comp_id = cmp.company_id 
CROSS APPLY (
    SELECT TOP(1) pr.todate
    FROM profile pr 
    INNER JOIN acondition ON as_id = as_ac_id 
    WHERE emp.acca_id = pr.profile_id AND (pr.ac_act_id = 20) AND as_closed = 0 
    ORDER BY pr.todate ASC
) AS ca