Is it possible to use FROM in PS query expression? If not is there an alternative solution? - peoplesoft

Question

I'm new with PS Query and SQL. I have a working SQL however I cannot translate it to PS Query.
So basically, I would like to present the comparison of my products and its amount per column.
Here are my sample data:
Product | Month | Amount
--------|-------|-------
Phone | 2 | 25
Laptop | 2 | 30
Phone | 1 | 20
Laptop | 1 | 40
Below is the code that I'm having hard time translating to PS Query:
Select ….
SUM(CASE WHEN Product1 <> Product2 AND Product2 = Laptop THEN 30
/*On my second statement, when the product are equal, i need to get the amount on the previous month.*/
WHEN Product1 = Product3 AND Product3 = Phone
THEN (SELECT Amount
FROM FINAL_TBL B
WHERE B.PERIOD = A.PERIOD - 1)
ELSE 0
END) AS Amount
From FINAL_TBL FTBL A
Where <Conditions>
My expected output should be
Product1 | Amount1 | Product2 | Amount2 | Product3 | Amount3
------------|-----------|-----------|-----------|-----------|--------
Phone | 25 | Laptop | 30 | Phone | 20

Answer 1

You cannot add a FROM in a PSQUERY expression.
The query you are trying to translate can be rewritten to:
Select *
SUM(CASE WHEN Product1 <> Product2 AND Product2 = Laptop
THEN 30
WHEN Product1 = Product3 AND Product3 = Phone
THEN B.Amount
ELSE 0
END) AS Amount
FROM FINAL_TBL A, FINAL_TBL B
WHERE B.PERIOD = A.PERIOD - 1
AND <Conditions>
But neither this or the original query would lead to the output you expect. What you are looking for is the PIVOT clause.

Answer 2

Whenever I run into a situation where I have a complicated query that's difficult or impossible to build through PSQuery, I make a view in App Designer that has the SQL.
Then make a PSQuery where you select from this view. I assume your <conditions> are user-entered data that you want to be entered when running the query, so add those conditions to the PSQuery that you build.
However, I think you should rethink what you're trying to do with your query. It looks like you're trying to list all products/prices that were bought in month X, as well as the price for the first product for month X - 1. With just two possible products (laptops and phones), this'll work, but when you start adding more types of products, you'll need more PRODUCT and PRICE columns. I don't think you'll be able to do that through PSQuery because you can't have a dynamic number of columns.
If you could explain what you're trying to accomplish and why, then someone might be able to suggest an alternative that'll work through PSQuery.