diff --git a/server/channels/store/sqlstore/channel_store_categories.go b/server/channels/store/sqlstore/channel_store_categories.go
index f35938d3c61..95502e2ab69 100644
--- a/server/channels/store/sqlstore/channel_store_categories.go
+++ b/server/channels/store/sqlstore/channel_store_categories.go
@@ -442,6 +442,8 @@ func (s SqlChannelStore) completePopulatingCategoryChannelsT(db dbSelecter, cate
 		return category, nil
 	}
 
+	isMySQL := s.DriverName() == model.DatabaseDriverMysql
+
 	var channelTypeFilter sq.Sqlizer
 	if category.Type == model.SidebarCategoryDirectMessages {
 		// any DM/GM channels that aren't in any category should be returned as part of the Direct Messages category
@@ -457,20 +459,40 @@ func (s SqlChannelStore) completePopulatingCategoryChannelsT(db dbSelecter, cate
 	}
 
 	// A subquery that is true if the channel does not have a SidebarChannel entry for the current user on the current team
-	doesNotHaveSidebarChannel := sq.Select("1").
-		Prefix("NOT EXISTS (").
-		From("SidebarChannels").
-		Join("SidebarCategories on SidebarChannels.CategoryId=SidebarCategories.Id").
-		Where(sq.And{
-			sq.Expr("SidebarChannels.ChannelId = ChannelMembers.ChannelId"),
-			sq.Eq{"SidebarCategories.UserId": category.UserId},
-			sq.Eq{"SidebarCategories.TeamId": category.TeamId},
-		}).
-		Suffix(")")
+	var doesNotHaveSidebarChannel sq.SelectBuilder
+	if isMySQL {
+		doesNotHaveSidebarChannel = sq.Select("/*+ QB_NAME(subq1) */ 1").
+			Prefix("NOT EXISTS (").
+			From("SidebarChannels").
+			// we have to use an index hint for MySQL.
+			Join("SidebarCategories USE INDEX(idx_sidebarcategories_userid_teamid) on SidebarChannels.CategoryId=SidebarCategories.Id").
+			Suffix(")")
+	} else {
+		doesNotHaveSidebarChannel = sq.Select("1").
+			Prefix("NOT EXISTS (").
+			From("SidebarChannels").
+			Join("SidebarCategories on SidebarChannels.CategoryId=SidebarCategories.Id").
+			Suffix(")")
+	}
+
+	doesNotHaveSidebarChannel = doesNotHaveSidebarChannel.Where(sq.And{
+		sq.Expr("SidebarChannels.ChannelId = ChannelMembers.ChannelId"),
+		sq.Eq{"SidebarCategories.UserId": category.UserId},
+		sq.Eq{"SidebarCategories.TeamId": category.TeamId},
+	})
 
 	channels := []string{}
+	var col string
+	if isMySQL {
+		// This is a materialization hint for MySQL to materialize
+		// the doesNotHaveSidebarChannel sub-query
+		// Without this hint, MySQL is unable to come up with this plan by itself.
+		col = "/*+ SEMIJOIN(@subq1 MATERIALIZATION) */ Id"
+	} else {
+		col = "Id"
+	}
 	sql, args, err := s.getQueryBuilder().
-		Select("Id").
+		Select(col).
 		From("ChannelMembers").
 		LeftJoin("Channels ON Channels.Id=ChannelMembers.ChannelId").
 		Where(sq.And{