join vs union
JOIN combines the ROWs, we will have longer rows at the end.
We are joining the rows from two or more related tables.
UNION combines the COLUMNs, we will have longer columns at the end.
UNION combine two different query.
We are joining the columns from two or more related tables.
Can be non related tables but queries must select same
column names with same data type.UNION ALL LEFT JOIN
SELECT
comments.*, users.company, users.contact_person, users.email
FROM
comments
LEFT JOIN users ON users.user_id = comments.user_id
WHERE
comment_id = %s
UNION ALL
SELECT activity.*, users.company, users.contact_person, users.email
FROM
activity
LEFT JOIN users ON users.user_id = activity.user_id
WHERE
comment_id = %s
ORDER BY
timestamp ASCCopyright © 2021 Codeinu
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