Question

我从四个不同的表中获取数据。这就是我的方式：

select value_split.id,
count(invoice_request.id) as counts,
GROUP_CONCAT(`category`.`category_name`) as `category_name`
from value_split
left join invoice_request
on invoice_request.id = value_split.id
and MONTH(invoice_request.from_date) = '05'
and YEAR(invoice_request.from_date) = '2016'
and invoice_request.status = '1'
left join `category_value` on value_split.id = category_value.id 
left join `category` on category_value.category_id = category.category_id
where MONTH(value_split.date) = '05'
and YEAR(value_split.date) = '2016'
group by value_split.id, value_split.date
limit  0, 2147483647

预期的答案是：

id|counts|category_name
1 |  1   | service, drop
2 |  2   | drop
3 |  1   | service

但是，我得到的是：

id|counts|category_name
1 |  5   | service, drop
2 |  4   | drop
3 |  5   | service

如果我删除第10行和第11行，我会得到正确答案。但是，如果我加入它们，我会得到错误的。但是，我也希望展示它。那么，我该怎么做才能获得正确的输出？这有什么问题？

Answer 1

使用

COUNT(DISTINCT invoice_request.id) AS counts,

在mysql中过滤没有重复

1 个答案: