I'd use Common Tables Expressions in composition with OLAP Functions
Mit freundlichen Grüßen / Best regards
Birgitta Hauser
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-----Original Message-----
From: RPG400-L <rpg400-l-bounces@xxxxxxxxxxxxxxxxxx> On Behalf Of Greg
Wilburn
Sent: Freitag, 6. März 2020 17:52
To: RPG programming on IBM i <rpg400-l@xxxxxxxxxxxxxxxxxx>
Subject: Most efficient SQL approach
I am rewriting an old RPG report using SQL (and SQL views I already have).
The "report" generates a database table as output
I need one row for each customer. In each row I need columns for several
sales figures that can be found in two other views.
I have SQL views for the Customer, Invoices and Orders.
I currently have it written where each sales figure is a separate
sub-select. Note that the "where" clause for each is slightly different.
It seems like this could be written more efficiently... but I'm not sure
what approach to take
1. Use common table expressions?
2. Create the output table, then use separate SQL expressions to insert
each of the summed values?
This is a simplified version of the code (for simplicity I've replaced the
RPG variables with constant values).
SELECT CUS.COM_NBR, CUS.CUST_NBR, CUS.CUST_NAME, (more here), (select
coalesce(sum(opn_amt),0) from V_ORDERS where com_nbr=cus.com_nbr and
ent_nbr=cus.ent_nbr and
ord_date>='2020-01-01' and ord_date<='2020-03-04') as BOOK_YTD,
(select coalesce(sum(shp_amt),0) from V_INVOICES where com_nbr=cus.com_nbr
and ent_nbr=cus.ent_nbr and
inv_date>='2020-01-01' and inv_date<='2020-03-04' )as NET_YTD,
(select coalesce(sum(shp_amt),0) from V_INVOICES where com_nbr=cus.com_nbr
and ent_nbr=cus.ent_nbr and
inv_date>='2019-01-01' and inv_date<='2019-03-04' ) as
PREV_YR_TOTAL, (select coalesce(sum(shp_amt),0) from V_INVOICES where
com_nbr=cus.com_nbr and ent_nbr=cus.ent_nbr and
inv_date>='2019-01-01' and inv_date<='2019-03-04' ) as
NET_PREV_YTD, (select coalesce(sum(ord_amt),0) from V_ORDERSA where
com_nbr=cus.com_nbr and ent_nbr=cus.ent_nbr and
ord_date>='2019-01-01' and ord_date<='2019-03-04') as BOOK_PREV_YTD
from V_CUSTMSTR as CUS where CUS.COM_NBR='012';
Thanks,
Greg
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