mysql select and count left join
select
t.Topic,
t.Title,
count(distinct s.starID) as StarCount,
count(distinct m.User) as UserCount,
count(distinct m.messageID) as MessageCount
from
Topics t
left join Messages m ON m.Topic = t.Topic
left join Stars_Given s ON s.Topic = t.Topic
group by
t.Topic,
t.Titlemultiple joins mysql
SELECT dashboard_data.headline, dashboard_data.message, dashboard_messages.image_id, images.filename
FROM dashboard_data
INNER JOIN dashboard_messages
ON dashboard_message_id = dashboard_messages.id
INNER JOIN images
ON dashboard_messages.image_id = images.image_idmysql left join multiple tables
-- LEFT OUTER JOIN is equivalent to LEFT JOIN
-- b.VALUE1 is null when ID not in table2 (idem for c.VALUE1 in table3)
SELECT a.ID, a.NAME, b.VALUE1, c.VALUE1 FROM table1 a
LEFT OUTER JOIN table2 b ON a.ID = b.ID
LEFT OUTER JOIN table3 c ON a.ID = c.ID
WHERE a.ID >= 1000;
-- ⇓ Test it ⇓ (Fiddle source link)Copyright © 2021 Codeinu
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