RE: Most efficient SQL approach

I try to avoid work files. If a CTE will get the job done, I'd say go for it. And as always, run your query thru VE.

HTH



-----Original Message-----
From: Greg Wilburn [mailto:gwilburn@xxxxxxxxxxxxxxxxxxxxxxx]
Sent: Friday, March 06, 2020 10:52 AM
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