Help - count function returns strange results

Question

hi everyone,
here's my scenario: i'm trying to get the NUMBER OF REPORTS and NUMBER OF
IMAGES GROUP BY MONTH from the two tables below.
REPORT
reportid(*primary key)
date
IMAGE
reportid(*foreign key referring to report's table)
image
sample output:
MONTH NO.OF REPORTS NO. OF IMAGES
feb 01 10 9
mar 01 12 8
my SQL goes like this:
select to_char(date, 'month-yy'),
count(REPORT.reportid), count(IMAGE.reportid)
from REPORT, IMAGE
where REPORT.reportid = IMAGE.reportid
group by to_char(date, 'month-yy')
the above sql yielded strange results, number of images is equal to the number of reports, which is of course wrong! as one report may or may not contain one or more image.
i dont know what's wrong with the above statement, but if i were to group it
by REPORTID and DAY rather than MONTH, then amazingly it works! what's
wrong with the count, why does it give me the same result if i group by
MONTH.
can anyone shed some light on this?

Answer 1

try using the following example:
Table TEST_REPORT
RPTID RPTDATE
1 02-JAN-01
3 02-JAN-01
2 02-JAN-01
5 11-FEB-01
6 11-FEB-01
7 11-FEB-01
Table TEST_IMAGE
RPTID IM
1 1
2 1
3 1
SQL:
select to_char(rptdate,'MON-YYYY'),
sum(decode(a.rptid,null,0,1)) report_cnt,
sum(decode(b.rptid,null,0,1)) image_cnt
from test_report a, test_image b
where a.rptid = b.rptid(+)
group by to_char(rptdate,'MON-YYYY');
<BLOCKQUOTE><font size="1" face="Verdana, Arial, Helvetica">quote:</font><HR>Originally posted by skcedric:
hi everyone,
here's my scenario: i'm trying to get the NUMBER OF REPORTS and NUMBER OF
IMAGES GROUP BY MONTH from the two tables below.
REPORT
reportid(*primary key)
date
IMAGE
reportid(*foreign key referring to report's table)
image
sample output:
MONTH NO.OF REPORTS NO. OF IMAGES
feb 01 10 9
mar 01 12 8
my SQL goes like this:
select to_char(date, 'month-yy'),
count(REPORT.reportid), count(IMAGE.reportid)
from REPORT, IMAGE
where REPORT.reportid = IMAGE.reportid
group by to_char(date, 'month-yy')
the above sql yielded strange results, number of images is equal to the number of reports, which is of course wrong! as one report may or may not contain one or more image.
i dont know what's wrong with the above statement, but if i were to group it
by REPORTID and DAY rather than MONTH, then amazingly it works! what's
wrong with the count, why does it give me the same result if i group by
MONTH.
can anyone shed some light on this? <HR></BLOCKQUOTE>
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