Question

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:

UPDATE sales SET status = 'ACTIVE' WHERE id IN (SELECT DISTINCT (saleprice, saledate), id, count(id)              FROM sales              HAVING count = 1) 

But my brain hurts going any farther than that.

Answer 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  )