Looping SQL Script with Multiple Select Queries - sql

Question

I have a very specific problem relating to a query I am trying to write.
Basically the inventory table has about 450,000 rows of inventory items, showing the closing balance of each item of inventory for the end of each month. The other tables include a shipping table, which tracks daily data for all items of inventory coming in and leaving a specific location. Then we also have a production table, that tracks items of inventories that are used in the production process daily.
We are trying to create another table that tracks Weekly Inventories using the Shipping and Production Tables, and then calculating an end of month variance.
Here is my Pseudocode for the script I have had to write:
FOR EACH ROW IN INVENTORY_TABLE
#incoming_shipping = SELECT INCOMING_AMOUNT FROM SHIPPING_TABLE WHERE WEEK_OF_MONTH = 1
#outgoing_shipping = SELECT OUTGOING_AMOUNT FROM SHIPPING_TABLE WHERE WEEK_OF_MONTH = 1
#outgoing_production =SELECT OUTGOING_AMOUNT FROM PRODUCTION TABLE WHERE WEEK_OF_MONTH = 1
#closing_inventory=ROW.OpeningAmount + #incoming_shipping - #outgoing_shipping + #outgoing_production
INSERT INTO WEEKLY_INVENTORY (Opening_Amount,Closing_Amount)
'Compute Week 2 Value
#incoming_shipping = SELECT INCOMING_AMOUNT FROM SHIPPING_TABLE WHERE WEEK_OF_MONTH = 2
#outgoing_shipping = SELECT OUTGOING_AMOUNT FROM SHIPPING_TABLE WHERE WEEK_OF_MONTH = 2
#outgoing_production =SELECT OUTGOING_AMOUNT FROM PRODUCTION TABLE WHERE WEEK_OF_MONTH = 2
#closing_inventory=ROW.OpeningAmount + #incoming_shipping - #outgoing_shipping + #outgoing_production
INSERT INTO WEEKLY_INVENTORY (Opening_Amount,Closing_Amount)
'Continue doing this for the Four, Maybe 5 weeks that occur in a month.
NEXT
While it is correct, the query is a nightmare to execute and currently runs approximately 100 rows a minute. I have tried using Loops without Cursors, Cursors etc. and there is no obvious performance difference. I am wondering if there is a better way to write the script without using any Loops.
Thanks in advance for any help.

Answer 1

I believe something in the lines of would work for you:
INSERT INTO WEEKLY_INVENTORY(Opening_Amount, Closing_Amount)
SELECT
OPENING_AMOUNT,
(OPENING_AMOUNT +
(SELECT INCOMING_AMOUNT
FROM SHIPPING_TABLE
WHERE WEEK_OF_MONTH = ST.WEEK_OF_MONTH)
) - (
(SELECT OUTGOING_AMOUNT
FROM SHIPPING TABLE
WHERE WEEK_OF_MONTH = ST.WEEK_OF_MONTH) +
(SELECT OUTGOING_AMOUNT
FROM PRODUCTION_TABLE
WHERE WEEK_OF_MONTH = ST.WEEK_OF_MONTH)
)
FROM SHIPPING_TABLE ST
WHERE ST.WEEK_OF_MONTH <= 5
You don't have to loop over all rows in order to do this. You can calculate for each WEEK_OF_MONTH the value that needs to be inserted into WEEKLY_INVENTORY by using a combination of INSERT INTO SELECT.
In the SELECT part you build the values, for each week of month by using other SELECT statements to determine the value for Closing_Amount.
The above query would be a straightforward option from your code, but the same functionality as above can be achieved, with an increase in speed by using a JOIN, with the below query:
INSERT INTO WEEKLY_INVENTORY(Opening_Amount, Closing_Amount)
SELECT
ST.OPENING_AMOUNT
, (ST.OPENING_AMOUNT + ST.INCOMING_AMOUNT)-(ST.OUTGOING_AMOUNT + PT.OUTGOING_AMOUNT)
FROM SHIPPING_TABLE ST
INNER JOIN PRODUCTION_TABLE PT ON ST.WEEK_OF_MONTH = PT.WEEK_OF_MONTH
Depending on how your database schema is structured, the queries above might not work as you might need to use an aggregate function, SUM() I assume and also GROUPing BY product. But using just the pseudocode you provided, this is the translation into SQL.