如何以laravel方式组合两个查询

Posted 2023-02-16

【中文标题】如何以laravel方式组合两个查询

【英文标题】：how to combine two queries in larvel way

【发布时间】：2021-10-12 20:34:43

【问题描述】：

我有 3 张桌子：

tb_user tb_addquestion tb_answer

以下查询返回每个用户的问题计数 (query 1) 和每个用户的答案 (query 2)。我需要将结果合并到一个输出中。

如何在单个查询的帮助下实现这一目标？

每位用户的问题数 (query1)

SELECT tb_addquestion.userid,
       COUNT(*) AS count
FROM tb_addquestion
LEFT JOIN tb_user
    ON tb_user.userid = tb_addquestion.userid
GROUP BY tb_addquestion.userid
HAVING count > 0 AND
       count < 15 

每个用户的答案 (query2)

SELECT tb_answer.userid,
       COUNT(*) AS count
FROM tb_answer
LEFT JOIN tb_user
    ON tb_user.userid = tb_answer.userid
GROUP BY tb_answer.userid
HAVING count > 0 AND
       count < 15 

【问题讨论】：

抱歉，运行 2 个单独的查询有什么问题？如果将它们组合起来，它们仍将作为 2 个查询运行（如果可以组合它们）。

@matiaslauriti 您确定两个单独的查询（= 两个数据库请求）和一个组合查询（= 一个数据库请求）之间没有区别（在性能方面）吗？

@AbsoluteBeginner 数据库性能将是相同的，或者将它们加入同一个查询中，将是最糟糕的......

【参考方案1】：

你可以使用UNION:

SELECT tb_addquestion.userid,
       COUNT(*) AS count,
       'questions' AS type
FROM tb_addquestion
LEFT JOIN tb_user
    ON tb_user.userid = tb_addquestion.userid
GROUP BY tb_addquestion.userid
HAVING count > 0 AND
       count < 15 

UNION

SELECT tb_answer.userid,
       COUNT(*) AS count,
       'answers' AS type
FROM tb_answer
LEFT JOIN tb_user
    ON tb_user.userid = tb_answer.userid
GROUP BY tb_answer.userid
HAVING count > 0 AND
       count < 15 

【参考方案2】：

通常我们会在单独的子查询中执行聚合，然后将主表连接到每个子查询：

SELECT
    u.userid,
    COALESCE(aq.q_cnt, 0) AS q_cnt,
    COALESCE(a.a_cnt, 0) AS a_cnt
FROM tb_user u
LEFT JOIN
(
    SELECT userid, COUNT(*) AS q_cnt
    FROM tb_addquestion
    GROUP BY userid
    HAVING q_cnt > 0 AND q_cnt < 15
) aq
    ON aq.userid = u.userid
LEFT JOIN
(
    SELECT userid, COUNT(*) AS a_cnt
    FROM tb_answer
    GROUP BY userid
    HAVING a_cnt > 0 AND a_cnt < 15
) a
    ON a.userid = u.userid