SQL Case Update to two different column based on select - sql

Question

I'm trying to perform what I believe a very simple case-update SQL to two different column based on a select:
PROD_TB:
Product_Code Reg_Price Sale_Price
A 1000 2000
PRICE_TB:
Product_Code Type Price
A REG 3000
A SALE 4000
Desired update result:
PROD_TB:
Product_Code Reg_Price Sale_Price
A 3000 4000
What I attempted:
UPDATE PROD_TB
SET Reg_Price = CASE
WHEN PRICE_TB.Type = 'REG'
THEN PRICE_TB.Price
ELSE Reg_Price
END,
Sale_Price = CASE
WHEN PRICE_TB.Type = 'SALE'
THEN PRICE_TB.Price
ELSE Sale_Price
END
FROM
PROD_TB
JOIN
PRICE_TB ON PROD_TB.PRODUCT_CODE = PRICE_TB.PRODUCT_CODE
Running the above SQL only updates regular price, not the sale price. Does SQL not support these types of update query? Or did I make an elementary mistake?

Answer 1

Something like this? Basically, just join the set from the PRICE_TB on the condition of which column you want to get from it.
But this is assuming you will only ever have one PRICE_TB.TYPE per updated PROD_TB column name, and that each PROD_TB column always contains a value in PRICE_TB, otherwise it'll be NULL and that row won't be returned. So make sure you know the variations of data that can exist here.
UPDATE PROD
SET Reg_Price = REG.Price, Sale_Price = SALE.Price
FROM PROD_TB PROD
JOIN PRICE_TB REG ON REG.Product_Code = PROD.Product_Code AND REG.Type = 'REG'
JOIN PRICE_TB SALE ON SALE.Product_Code = PROD.Product_Code AND SALE.Type = 'SALE'

Answer 2

You need to get the data into one row first, here's example that fetches always the biggest price, in case there's more than one in PRICE_TB, otherwise it should work the same way as #Kahn's sql.
UPDATE
PROD
SET
PROD.Reg_Price = PRICE.Reg_Price,
PROD.Sales_Price = PRICE.Sales_Price
FROM PROD_TB PROD, cross apply (
select
max(CASE WHEN Type = 'REG' THEN Price ELSE 0 end) as Reg_Price,
max(CASE WHEN Type = 'SALE' THEN Price ELSE 0 end) as Sale_Price
from
PRICE_TB PRICE
where
PRICE.Product_Code = PROD.Product_Code
) PRICE

Answer 3

If your table PRICE_TB doesn't always contain both values, you could use this to make sure the table is updated anyway:
UPDATE t1
SET
Reg_Price = coalesce(t2.Price, t1.Reg_Price),
Sale_Price = coalesce(t3.Price, t1.Sale_Price)
FROM PROD_TB t1
LEFT JOIN
PRICE_TB t2
ON
t1.ProductCode = t2.ProductCode AND
t2.[Type] = 'REG'
LEFT JOIN
PRICE_TB t3
ON
t1.ProductCode = t3.ProductCode AND
t3.[Type] = 'SALE'
WHERE
t2.[Type] = 'REG' OR
t3.[Type] = 'SALE'