To delete posts in a channel older than XX days I did this because the timestamps are in milliseconds:

delete from Posts where ChannelId='laskjdflasjkfas78f7asf73uh' AND CreateAt < (1000 * UNIX_TIMESTAMP(DATE_SUB(NOW(),INTERVAL 30 DAY))) ;

The channel id can be fetched using the "About" entry in the dropdown menu.

At the SQL query level, list the posts posted by a given incoming webhook

(psql) # \x on

# SELECT p.*
FROM Posts p
JOIN Channels c ON p.channelid=c.id
JOIN Teams t ON p.teamid=t.id
WHERE t.displayname='teamname_at_topleft'
AND c.displayname='channelname_at_topmiddle'
AND props LIKE '%"from_webhook":"true"%'
AND props LIKE '%"override_username":"lowercasehookname"%';

After checking what it yielded, you can use that as a subquery:

DELETE FROM Posts WHERE id IN (SELECT p.id FROM .....)

you may tweak the query if you want to target a given userid.

It doesn't handle/fix posts whose parentid point to one of the deleted posts.and thread membership

An update:

mysql>

DELETE FROM mattermost.Posts WHERE Posts.ChannelId = 'nkx56xy6xpbrjx98p1ggpyug3o';

You should change the 'ChannelId' ofcouse.

Hello, a simple SQL query can be used. However be careful it will delete all posts from specific channel

DELETE
FROM PUBLIC.POSTS
WHERE CHANNELID = '<enter channel id here>'

Specially when a channel is used only for notifications from other places.

Clean Channel, yes. Good idea !

A simple button for the admin of the channel to clean complete history of the channel would really be cool.