Doing a count from a join which includes zeros

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Doing a count from a join which includes zeros

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Topic

everbright
Starting Member

1 Post

Posted - 2007-04-20 : 00:58:25

Hi all,

I have 2 tables as follows:
Table A
id name department
1 Kev OSD
2 Roger LPD
3 Bim PWD
4 Conny PWD
5 Dan CPD

Table B
id table_a_id logindate
1 5 17/04/2007
2 1 16/04/2007
3 2 15/04/2007
4 2 16/04/2007

I want to form a query that retrives a count of unique user logins by departments, for a range of login dates.

So if I run the query for logins before 18/04/2007. I should get the following results

A.department Logins
OSD 1
LSD 1
PWD 0
CPD 1

Note that the count for LSD should be 1, although Kev logged in twice in the time period.

I tried some queries, but none was able to give me what I want. Most of these queries will drop the departments with no logins at all (i.e. no corresponding entries in table B).

Here's what I tried:

select A.department, count(distinct B.table_a_id) from A left outer join B on A.id=B.table_a_id where logindate < convert(datetime, '18/04/2007', 103) group by department

Anyone has done something similar and succeeded in getting the results?

Appreciate any help with this! Thanks!

khtan
In (Som, Ni, Yak)

17689 Posts

Posted - 2007-04-20 : 03:57:19

use LEFT JOIN


select A.department, Logins = isnull(B.id, 0)
from   tablea A left join talbeb B
on  A.id = B.id

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