I need to retrieve all rows from a table where 2 columns combined are all different. So I want all the sales that do not have any other sales that happened on the same day for the same price. The sales that are unique based on day and price will get updated to an active status.
So I'm thinking:
SET status = 'ACTIVE'
WHERE id IN (SELECT DISTINCT (saleprice, saledate), id, count(id)
HAVING count = 1)
SELECT DISTINCT a,b,c FROM t
is roughly equivalent to:
SELECT a,b,c FROM t GROUP BY a,b,c
It's a good idea to get used to the GROUP BY syntax, as it's more powerful.
For your query, I'd do it like this:
UPDATE sales SET status='ACTIVE' WHERE id IN ( SELECT id FROM sales S INNER JOIN ( SELECT saleprice, saledate FROM sales GROUP BY saleprice, saledate HAVING COUNT(*) = 1 ) T ON S.saleprice=T.saleprice AND s.saledate=T.saledate )