Question

我尝试配置子查询，但在聚合/分组方面遇到了一些困难。子查询根据平均值选择计数。但是，将AVG(response) >= target条件放在 WHERE 块中会导致＆＃34;无效使用组功能＆＃34;错误。将条件放在子查询的 HAVING 块中，除了它需要目标变量必须出现在 SELECT 块中COUNT，导致操作数应包含1列＆＃34;错误。查询的副本如下。

我熟悉嵌套查询和聚合函数，但这种特殊组合拒绝合作。似乎应该有一个关键字＆＃34;选择此字段进行比较/ HAVING但不要将其返回＆＃34;，或者我可能只是错误地制定了查询。不幸的是，这是由BIRT报告软件运行的，所以我不能（据我所知）抓取原始数据并手动聚合。

查询（为清晰起见略微修剪）如下：

SELECT 
    c.job_competency_id,
    (
        SELECT 
            COUNT(ar1.assessment_result_id) 
        FROM 
            recent_assessment AS ra1,
            assessment_result AS ar1,
            client_job_competency AS jc1
        WHERE 
            ar1.assessment_id = a.assessment_id
            AND ra1.assessment_id = ar1.assessment_id
            AND ar1.job_competency_id = jc1.job_competency_id
            AND ar1.job_competency_id = c.job_competency_id
            AND AVG(ar1.response) >= jc1.target
        GROUP BY jc1.job_competency_id
    ) AS n_meets
FROM 
    recent_assessment AS ra,
    assessment AS a,
    assessment_result AS ar,
    client_job_competency AS jc,
    job_competency AS c,
    master_competency AS mc 
WHERE 
    a.client_id = ?
    AND ra.assessment_id = a.assessment_id
    AND ar.assessment_id = a.assessment_id
    AND c.job_competency_id = ar.job_competency_id
    AND c.master_competency_id = mc.master_competency_id
    AND jc.job_competency_id = c.job_competency_id;

如果重要，替代子查询就在这里：

    (
        SELECT 
            COUNT(ar1.assessment_result_id),
            jc1.target
        FROM 
            recent_assessment AS ra1,
            assessment_result AS ar1,
            client_job_competency AS jc1
        WHERE 
            ar1.assessment_id = a.assessment_id
            AND ra1.assessment_id = ar1.assessment_id
            AND ar1.job_competency_id = jc1.job_competency_id
            AND ar1.job_competency_id = c.job_competency_id
        GROUP BY jc1.job_competency_id
        HAVING AVG(ar1.response) >= jc1.target
    ) AS n_meets

如果你读到这里，谢谢你看看。如果有任何要求澄清，请告诉我。希望我在某个地方犯了一个愚蠢的错误。

Answer 1

您不能在WHERE子句中使用聚合函数，因为在选择所有行之前它不会处理聚合，这就是WHERE子句确实

要解决HAVING要求您选择要与之比较的列的问题，可以将其包装在另一级子查询中。然后外部查询可以返回您要放入SELECT列表的一列。

(SELECT n_meets
FROM (
    SELECT 
        COUNT(ar1.assessment_result_id) AS n_meets,
        jc1.target
    FROM 
        recent_assessment AS ra1,
        assessment_result AS ar1,
        client_job_competency AS jc1
    WHERE 
        ar1.assessment_id = a.assessment_id
        AND ra1.assessment_id = ar1.assessment_id
        AND ar1.job_competency_id = jc1.job_competency_id
        AND ar1.job_competency_id = c.job_competency_id
    GROUP BY jc1.job_competency_id
    HAVING AVG(ar1.response) >= jc1.target
) AS x) AS n_meets

MySQL嵌套查询HAVING Field

1 个答案: