altering query in db2 to fix count from a join - sql

Question

I'm getting an aggregated count of records for orders and I'm getting the expected count on this basic query:
SELECT
count(*) as sales_180,
180/count(*) as velocity
FROM custgroup g
WHERE g.cstnoc = 10617
AND g.framec = 4847
AND g.covr1c = 1763
AND g.colr1c = 29
AND date(substr(g.extd1d,1,4)||'-'||substr(g.EXTD1d,5,2)||'-'||substr(g.EXTD1d,7,2) ) between current_Date - 180 DAY AND current_Date
But as soon as I add back in my joins and joined values then my count goes from 1 (which it should be) to over 200. All I need from these joins is the customer ID and the manager number. so even if my count is high, I'm basically just trying to say "for this cstnoc, give me the slsupr and xlsno"
How can I perform this below query without affecting the count? I only want my count (sales_180 and velocity) coming from the custgroup table based on my where clause, but I then just want one value of the xcstno and xslsno based on the cstnoc.
SELECT
count(*) as sales_180,
180/count(*) as velocity,
c.xslsno as CustID,
cr.slsupr as Manager
FROM custgroup g
inner join customers c
on g.cstnoc = c.xcstno
inner join managers cr
on c.xslsno = cr.xslsno
WHERE g.cstnoc = 10617
AND g.framec = 4847
AND g.covr1c = 1763
AND g.colr1c = 29
AND date(substr(g.extd1d,1,4)||'-'||substr(g.EXTD1d,5,2)||'-'||substr(g.EXTD1d,7,2) ) between current_Date - 180 DAY AND current_Date
GROUP BY c.xslsno, cr.slsupr

Answer 1

You are producing multiple rows when joining, so your count is now counting all the resulting rows with all that [unintended] multiplicity.
The solution? Use a table expression to pre-compute your count, and then you can join it to the other tables, as in:
select
g2.sales_180,
g2.velocity,
c.xslsno as CustID,
cr.slsupr as Manager
from customers c
join managers cr on c.xslsno = cr.xslsno
join ( -- here the Table Expression starts
SELECT
count(*) as sales_180,
180/count(*) as velocity
FROM custgroup g
WHERE g.cstnoc = 10617
AND g.framec = 4847
AND g.covr1c = 1763
AND g.colr1c = 29
AND date(substr(g.extd1d,1,4)||'-'||substr(g.EXTD1d,5,2)
||'-'||substr(g.EXTD1d,7,2) )
between current_Date - 180 DAY AND current_Date
) g2 on g2.cstnoc = c.xcstno
You can also use a Common Table Expression (CTE) that will produce the same result:
with g2 as (
SELECT
count(*) as sales_180,
180/count(*) as velocity
FROM custgroup g
WHERE g.cstnoc = 10617
AND g.framec = 4847
AND g.covr1c = 1763
AND g.colr1c = 29
AND date(substr(g.extd1d,1,4)||'-'||substr(g.EXTD1d,5,2)
||'-'||substr(g.EXTD1d,7,2) )
between current_Date - 180 DAY AND current_Date
)
select
g2.sales_180,
g2.velocity,
c.xslsno as CustID,
cr.slsupr as Manager
from customers c
join managers cr on c.xslsno = cr.xslsno
join g2 on g2.cstnoc = c.xcstno