db/migrations: ensure to drop parentid from posts table (#21493)

db/migrations/migrations.list

@@ -188,6 +188,8 @@ db/migrations/mysql/000093_notify_admin.down.sql
 db/migrations/mysql/000093_notify_admin.up.sql
 db/migrations/mysql/000094_threads_teamid.down.sql
 db/migrations/mysql/000094_threads_teamid.up.sql
+db/migrations/mysql/000095_remove_posts_parentid.down.sql
+db/migrations/mysql/000095_remove_posts_parentid.up.sql
 db/migrations/postgres/000001_create_teams.down.sql
 db/migrations/postgres/000001_create_teams.up.sql
 db/migrations/postgres/000002_create_team_members.down.sql
@@ -376,3 +378,5 @@ db/migrations/postgres/000093_notify_admin.down.sql
 db/migrations/postgres/000093_notify_admin.up.sql
 db/migrations/postgres/000094_threads_teamid.down.sql
 db/migrations/postgres/000094_threads_teamid.up.sql
+db/migrations/postgres/000095_remove_posts_parentid.down.sql
+db/migrations/postgres/000095_remove_posts_parentid.up.sql

db/migrations/mysql/000095_remove_posts_parentid.down.sql

@@ -0,0 +1 @@
+-- Intentionally left blank as forward migration is not reversible.

db/migrations/mysql/000095_remove_posts_parentid.up.sql

@@ -0,0 +1,17 @@
+-- While upgrading from 5.x to 6.x with manual queries, there is a chance that this
+-- migration is skipped. In that case, we need to make sure that the column is dropped.
+
+SET @preparedStatement = (SELECT IF(
+    (
+        SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS
+        WHERE table_name = 'Posts'
+        AND table_schema = DATABASE()
+        AND column_name = 'ParentId'
+    ) > 0,
+    'ALTER TABLE Posts DROP COLUMN ParentId;',
+    'SELECT 1'
+));
+
+PREPARE alterIfExists FROM @preparedStatement;
+EXECUTE alterIfExists;
+DEALLOCATE PREPARE alterIfExists;

db/migrations/postgres/000095_remove_posts_parentid.down.sql

@@ -0,0 +1 @@
+-- Intentionally left blank as forward migration is not reversible.

db/migrations/postgres/000095_remove_posts_parentid.up.sql

@@ -0,0 +1,4 @@
+-- While upgrading from 5.x to 6.x with manual queries, there is a chance that this
+-- migration is skipped. In that case, we need to make sure that the column is dropped.
+
+ALTER TABLE posts DROP COLUMN IF EXISTS parentid;