1ALTER TABLE channels ADD COLUMN parent_path TEXT;
 2
 3UPDATE channels
 4SET parent_path = substr(
 5    channel_paths.id_path,
 6    2,
 7    length(channel_paths.id_path) - length('/' || channel_paths.channel_id::text || '/')
 8)
 9FROM channel_paths
10WHERE channel_paths.channel_id = channels.id;
11
12CREATE INDEX "index_channels_on_parent_path" ON "channels" ("parent_path");