Question

The following query is pulling duplicate site_ids, with me using DISTINCT I can’t figure out why…

SELECT
    DISTINCT site_id,
    deal_woot.*,
    site.woot_off,
    site.name AS site_name
FROM deal_woot
INNER JOIN site ON site.id = site_id
WHERE site_id IN (2, 3, 4, 5, 6)
ORDER BY deal_woot.id DESC LIMIT 5

Answer 1

DISTINCT looks at the entire record, not just the column directly after it. To accomplish what you want, you’ll need to use GROUP BY:

Non-working code:

SELECT
    site_id,
    deal_woot.*,
    site.woot_off,
    site.name AS site_name
FROM deal_woot
INNER JOIN site ON site.id = site_id
WHERE site_id IN (2, 3, 4, 5, 6)
GROUP BY site_id

Why doesn’t it work? If you GROUP BY a column, you should use an aggregate function (such as MIN or MAX) on the rest of the columns — otherwise, if there are multiple site_woot_offs for a given site_id, it’s not clear to SQL which of those values you want to SELECT.

You will probably have to expand deal_woot.* to list each of its fields.

Side-note: If you’re using MySQL, I believe it’s not technically necessary to specify an aggregate function for the remaining columns. If you don’t specify an aggregate function for a column, it chooses a single column value for you (usually the first value in the result set).