SELECT MIN value with GROUP BY and INNER JOIN?

Question

I have a query pulling data from 4 different tables;

SELECT cd.name, tt.card_number, tt.deck_count, tcg.url, MIN(tcgp.marketPrice) as 'price'
FROM card_occurrences tt
INNER JOIN card_database cd ON tt.card_number = cd.id
INNER JOIN tcgplayer_cards tcg ON cd.name = tcg.name
INNER JOIN tcgplayer_set_prices tcgp ON tcgp.productId = tcg.productID
GROUP BY tt.card_number
ORDER BY tt.deck_count DESC LIMIT 100

However, the tcg.url is wrong and I know it's a result of using MIN(tcgp.marketPrice) with GROUP BY .

If I exclude the MIN and `GROUP BY then I get the ungrouped results like so:

However, when I do MIN with GROUP BY then I am correctly getting the lowest price but the URL is wrong. It's getting the first one found.

I think I need to use another JOIN statement (or maybe a subquery?) but I'm not entirely sure. Some prodding in the right direction is welcome!

Answer 1

If you're using MySQL v8+ (or MariaDB 10.2+), then I think you should try using ROW_NUMBER() . Consider this example:

SELECT cd.name, tt.card_number, tt.deck_count, tcg.url, tcgp.marketPrice as 'price',
       ROW_NUMBER() OVER (PARTITION BY cd.name, tt.card_number ORDER BY tcgp.marketPrice) rn
FROM card_occurrences tt
INNER JOIN card_database cd ON tt.card_number = cd.id
INNER JOIN tcgplayer_cards tcg ON cd.name = tcg.name
INNER JOIN tcgplayer_set_prices tcgp ON tcgp.productId = tcg.productID;

The ROW_NUMBER() OVER (PARTITION BY cd.name, tt.card_number ORDER BY tcgp.marketPrice) rn function is assigning row number to the row value based on tcgp.marketPrice ascending while retaining the corresponding column value for the row.

Demo fiddle