查询结果乘以2

Question

3个表格。 app_forms, app_results, app_exhibitions

我想获得表单ID，表单名称，结果数量以及链接到表单的展览数量。目前，我得到这个查询：

SELECT 
f.id as id, 
f.name as formname, 
count(res.form_id) as resultcount, 
group_concat(b.name separator ', ') as exhibitionname 
FROM app_forms f 
LEFT JOIN app_results res ON f.id = res.form_id 
LEFT JOIN app_exhibitions exh ON exh.form_id = f.id 
GROUP by f.id 

问题是，它乘的事情由2.因为我也有4个exhbitions的CONCAT组（而不是2）分组和我有4个结果，而不是2计数组。我被困在如何解决这个问题上，这可能与杜贝左派加盟有关。

Answer 1

最简单的解决办法是在计数使用DISTINCT，如果你有例如app_results.id您app_results表的主键：

SELECT 
    f.id as id, 
    f.name as formname, 
    count(DISTINCT res.id) as resultcount, 
    group_concat(b.name separator ', ') as exhibitionname 
FROM 
    app_forms f LEFT JOIN app_results res ON f.id = res.form_id 
    LEFT JOIN app_exhibitions exh ON exh.form_id = f.id 
GROUP by f.id 

或加入一个已经分组表（我设B .name是exh.name）：

SELECT 
    f.id as id, 
    f.name as formname, 
    count(res.form_id) as resultcount, 
    exh.exhibitionname 
FROM 
    app_forms f LEFT JOIN app_results res ON f.id = res.form_id 
    LEFT JOIN (
    SELECT form_id, group_concat(name separator ', ') as exhibitionname 
    FROM app_exhibitions 
    GROUP BY form_id 
) exh ON exh.form_id = f.id 
GROUP by f.id