sql-server - 选择另一个相关列的总计为 0 的列

Question

我有一个名为 xDays 的表，设置如下:

╔══════════════╦═════════════════════════╦═══════╗
║ Project_Name ║          Date           ║ Hours ║
╠══════════════╬═════════════════════════╬═══════╣
║ proj1        ║ 2010-03-03 00:00:00.000 ║     0 ║
║ proj1        ║ 2010-03-04 00:00:00.000 ║     0 ║
║ proj1        ║ 2010-03-05 00:00:00.000 ║     0 ║
║ proj2        ║ 2010-03-03 00:00:00.000 ║     1 ║
║ proj2        ║ 2010-03-04 00:00:00.000 ║     0 ║
║ proj2        ║ 2010-03-05 00:00:00.000 ║     0 ║
╚══════════════╩═════════════════════════╩═══════╝

我想要做的是选择每个 Project_Name 中 Hours 列的总数为 0。在上面的例子中，select 语句应该返回 proj1，因为它的总 hours 是 0，而 proj2 的总时数是 1 .

我得到的最接近的是:

select sum(hours) as 'total', project_name
From xDays
group by project_name
order by project_name

这为我提供了一个表格，其中显示了每个 project_name 的总小时数，其中确实显示了某些 project_names 的 0 总小时数。从这里开始，我尝试了一些不同的东西，要么得到一个

Conversion failed when converting the varchar value to datatype int

错误或空结果。我尝试过的一些例子:

 select sum(hours) as 'total', project_name
 From xDays
 where 'total' = convert(varchar(10), 0)
 group by project_name
 order by project_name`

这将返回空结果。

select sum(hours) as 'total', project_name
From xDays
where 'total' = 0
group by project_name
order by project_name

这将返回转换错误(无法将 varchar total 转换为 int)。

我怎样才能让它正常工作？

Answer 1

您可以使用 HAVING 过滤聚合结果子句:

select sum(hours) as 'total'
From xDays
group by project_name
HAVING sum(hours) = 0
order by project_name

HAVING 子句只能出现在GROUP BY 子句之后，不能使用任何列别名