SQL Query based on a while loop - sql

Question

I am trying to construct an sql query using a while loop that increments a datetime by one minute each iteration and then generates a select statement based on the time:
declare #dt datetime
set #dt = '2011-7-21'
while #dt < '2011-7-22'
begin
select Count(*) From Actions Where Timestamp = #dt
set #dt = DATEADD(mi, 1, #dt)
end
The query works as intended except that every iteration of the while loop seems to produce a new query entirely, rather than simply a new row. Is there a way to construct this so that its one single query and each row is generated by the incrementation of the loop?
I believe this occurs because the select statement is inside the loop, but I'm not sure how to construct it a different way that works.
EDIT - Here is what I came up with using a temporary table, but it is slow. Maybe there is a faster way? If not thats fine, atleast this works:
create table #temp
(
[DT] datetime not null,
[Total] int not null
)
declare #dt datetime
declare #result int
set #dt = '2011-7-21'
while #dt < '2011-7-22'
begin
set #result = Count(*) From Actions Where Timestamp = #dt
insert #temp ([DT],[Total]) values (#dt, #result)
set #dt = DATEADD(mi, 1, #dt)
end
select * from #temp;
drop table #temp;

Answer 1

One way by using a table of numbers
declare #dt datetime
set #dt = '2011-07-21'
select DATEADD(mi, number, #dt)
from master..spt_values
where type = 'P'
and DATEADD(mi, number, #dt) < '2011-07-22'
If you have your own number table, use that
See here for more info http://wiki.lessthandot.com/index.php/Date_Ranges_Without_Loops
you full query would be like
DECLARE #dt DATETIME
SET #dt = '2011-07-21'
SELECT x.SomeTime,y.TheCount FROM
(SELECT DATEADD(mi, number, #dt) as SomeTime FROM master..spt_values
WHERE TYPE = 'P'
AND DATEADD(mi, number, #dt) < '2011-07-22') x
LEFT JOIN (
SELECT TIMESTAMP, COUNT(*) AS TheCount
FROM Actions
GROUP BY TIMESTAMP
) AS y
ON x.SomeTime = dateadd(mi, datediff(mi, 0, y.Timestamp)+0, 0)

Answer 2

If you have a numbers table (from 0 to a million or whatever), this is relatively simple:
SELECT *
FROM Numbers AS n
LEFT JOIN (
SELECT Timestamp, COUNT(*) AS Ct
FROM Actions
GROUP BY Timestamp
) AS ActionSummary
ON ActionSummary.Timestamp = DATEADD(mi, n.Number, '2011-07-21')
WHERE DATEADD(mi, n.Number, '2011-07-21') < '2011-07-22'
ORDER BY DATEADD(mi, n.Number, '2011-07-21')
No need for loops.
There's ways to optimize this, but that should be fairly understandable as it is.
Also note that the timestamps cannot have any seconds or fractions of a second for this to work (your original has this problem as well).