SQL Server：GROUP BY日期时间，没有刻度

Question

I have a query, that returns all entries, with unique datetime with ticks:

select t.date, count(*) as Count
    from table t
    group by t.date having count(*) = 1

I need a query that will return entries with unique datetime without ticks. To get datetime without ticks I'm using:

select CONVERT(VARCHAR(19), t.date, 120), count(*) as Count
from table t

So I'm expecting to use query:

select CONVERT(VARCHAR(19), t.date, 120), count(*) as Count
    from table t
    group by CONVERT(VARCHAR(19), t.date, 120) having count(*) = 1

But it throws an error:

Column "table.date" is invalid in the ORDER BY clause because it is not contained in either an aggregate function or the GROUP BY clause.

Do you have any idea what query should I use?

Answer 1

There are multiple possible datetime values in each group so instead of

ORDER BY t.date

you could use, for example

ORDER BY MIN(t.date)

to avoid this error.

Answer 2

This works fine:

select convert(varchar(19), t.date, 120), count(*) as count
from table t
group by convert(varchar(19), t.date, 120) 
having count(*) = 1
order by convert(varchar(19), t.date, 120) 

Answer 3

You have to ORDER BY an expression in the GROUP BY or an aggregation

ORDER BY
   CONVERT(VARCHAR(19), date, 120)

example:

SELECT
   ShorterDateTime, COUNT(*)
FROM
    (
    select CONVERT(VARCHAR(19), date, 120) AS ShorterDateTime
    from table
    ) t
GROUP BY
   ShorterDateTime
HAVING
   COUNT(*) > 1
ORDER BY
   ShorterDateTime