Group by date and count of entries - sql

Question

I'll make it short, the table looks like this:
| id (int) | registerDate (DATETIME)
|----------|-----------------
| 1 | 2014-07-29 12:00:00
| 2 | 2014-08-01 12:00:00
| 3 | 2014-08-01 12:00:00
| 4 | 2014-08-01 12:00:00
| 5 | 2014-08-02 12:00:00
| 6 | 2014-08-02 12:00:00
| 7 | 2014-08-04 12:00:00
If today is 2014-08-05, I want results like this:
| registerDate (DATETIME) | count (int)
| 2014-08-04 | 1
| 2014-08-03 | 0
| 2014-08-02 | 2
| 2014-08-01 | 1
| 2014-07-31 | 0
| 2014-07-30 | 0
| 2014-07-29 | 1
So I want the count of registered users in the past week (daily).
I tried to find it out on google (unsuccessfully) - however, I hope you can help.

Answer 1

SELECT registerDate, count(registerDate) FROM [TABLE] WHERE
registerDate between (GETDATE()-7) and GETDATE()
group by registerDate
order by registerDate desc
This will take a table like:
2 |1905-06-26 00:00:00.000
4 |2014-08-03 00:00:00.000
5 |2014-08-02 00:00:00.000
1 |2014-08-01 00:00:00.000
3 |2014-07-01 00:00:00.000
6 |2010-07-01 00:00:00.000
7 |2015-07-01 00:00:00.000
8 |2014-08-28 00:00:00.000
9 |2014-08-26 00:00:00.000
10 |2014-08-26 00:00:00.000
And create:
2014-08-28 00:00:00.000 | 1
2014-08-26 00:00:00.000 | 2
The problem with this is it doesn't show the days that are not in the table.
Give me a little more time, I'll have an updated version.
EDIT:
Now the more complex one...
-- Declare how far back you want to go
DECLARE #DAYSBACK int = 6
-- Select into a temptable
select CONVERT(date, registerDate) as RegDate, count(registerDate) as DateCount
INTO #temptable
from Temp where registerDate between (GETDATE()-6) and GETDATE()
group by registerDate order by registerDate desc
-- Check to see if exists if not, insert row
WHILE #DAYSBACK >= 0 BEGIN
IF NOT EXISTS (select top 1 1 from #temptable
where RegDate= CONVERT(date, (GETDATE()-#DAYSBACK))
group by RegDate)
INSERT INTO #temptable values ((GETDATE()-#DAYSBACK), 0)
SET #DAYSBACK = #DAYSBACK -1
END
-- Select what you want
select * from #temptable order by RegDate desc
-- Drop the table you created.
DROP TABLE #temptable
Using the same table as above, it will output:
Register Date | Date Count
--------------------------
2014-08-28 | 1
2014-08-27 | 0
2014-08-26 | 2
2014-08-25 | 0
2014-08-24 | 0
2014-08-23 | 0
2014-08-22 | 0

Answer 2

Try something like this:
select registerDate = convert(date,t.registerDate) ,
registrations = count(*)
from dbo.my_special_registration_table t
where t.registrationDate >= dateadd(day,-7,convert(date,getdate()))
group by convert(date,t.registerDate)
order by 1
If you try to filter out registrations older than 7 days using something like datediff():
where datediff(day,t.registrationDate,getdate()) <= 7
you turned the column registrationDate into an expression. As a result the query optimizer can't make use of any indices that might apply, thus forcing a table scan. If you table is large, performance is likely to be ... suboptimal.