我需要计算计数的项目

Question

的百分比我有两个表：

1：原因

id | title 
--------------------------------- 
1 | Customer didn't like it 
2 | Needs improving   
3 | Wrong format 

第二：项目

id | title  | rejected 
------------------------------------ 
1 | Priject 1 | Null 
2 | Priject 2 | 1 
3 | Priject 3 | 1 
4 | Priject 4 | Null 
5 | Priject 5 | 2 

我需要显示Reasons.Title和数量项目因此被拒绝。我已经成功地加入这些表一起，与此代码

SELECT reasons.title as title, count(*) as num 
FROM reasons 
LEFT JOIN reasons on projects.rejected = reasons.id 
WHERE projects.rejectedIS NOT NULL 
GROUP BY projects.rejected 

现在我需要添加比例，所以我最后的表看起来像这样

title     | num | percentage 
-------------------------------------------------- 
Customer didn't like it | 2  | 66,6 
Needs improving   | 1  | 33,3 

百分比的格式，当然并不重要。 我希望得到这个与MySQL完成的，所以我并不需要使用两个查询和额外的PHP，但如果有另一种解决方案，其他从MySQL，我愿意听听建议

Answer 1

你可以做这个由FROM子句中获得总：

SELECT r.title as title, count(*) as num, 
     COUNT(*)/pp.cnt as ratio 
FROM reasons r JOIN 
    projects p 
    ON p.rejected = r.id CROSS JOIN 
    (SELECT COUNT(*) as cnt FROM projects p WHERE rejects IS NOT NULL) pp 
GROUP BY r.title, pp.cnt; 

注：

• 这修复表名，因此查询有projects表。
• 这将删除WHERE，因为它不是必需的。
• 这将LEFT JOIN更改为内部联接。