MM-55295: Improve DB performance of some (Take 2) (#25865)

* Revert "Revert "MM-55295: Improve DB performance of some APIs (#25318)" (#25852)"

This reverts commit 077221a940.

* Fix the issue

```release-note
NONE
```

* lint fix

```release-note
NONE
```

server/channels/store/sqlstore/channel_store.go

@@ -1126,26 +1126,16 @@ func (s SqlChannelStore) GetChannelsByUser(userId string, includeDeleted bool, l
 	return channels, nil
 }
 
-func (s SqlChannelStore) GetAllChannelMembersById(channelID string) ([]string, error) {
-	sql, args, err := s.channelMembersForTeamWithSchemeSelectQuery.Where(sq.Eq{
-		"ChannelId": channelID,
-	}).ToSql()
-	if err != nil {
-		return nil, errors.Wrap(err, "GetAllChannelMembersById_ToSql")
-	}
-
-	dbMembers := channelMemberWithSchemeRolesList{}
-	err = s.GetReplicaX().Select(&dbMembers, sql, args...)
+func (s SqlChannelStore) GetAllChannelMemberIdsByChannelId(channelID string) ([]string, error) {
+	userIDs := []string{}
+	err := s.GetReplicaX().Select(&userIDs, `SELECT UserId
+		FROM ChannelMembers
+		WHERE ChannelId=?`, channelID)
 	if err != nil {
 		return nil, errors.Wrapf(err, "failed to get ChannelMembers with channelID=%s", channelID)
 	}
 
-	res := make([]string, len(dbMembers))
-	for i, member := range dbMembers.ToModel() {
-		res[i] = member.UserId
-	}
-
-	return res, nil
+	return userIDs, nil
 }
 
 func (s SqlChannelStore) GetAllChannels(offset, limit int, opts store.ChannelSearchOpts) (model.ChannelListWithTeamData, error) {
@@ -2070,6 +2060,20 @@ func (s SqlChannelStore) GetMember(ctx context.Context, channelID string, userID
 	return dbMember.ToModel(), nil
 }
 
+func (s SqlChannelStore) GetMemberLastViewedAt(ctx context.Context, channelID string, userID string) (int64, error) {
+	var lastViewedAt int64
+	if err := s.DBXFromContext(ctx).Get(&lastViewedAt, `SELECT COALESCE(LastViewedAt, 0) AS LastViewedAt
+		FROM ChannelMembers
+		WHERE ChannelId=? AND UserId=?`, channelID, userID); err != nil {
+		if err == sql.ErrNoRows {
+			return 0, store.NewErrNotFound("LastViewedAt", fmt.Sprintf("channelId=%s, userId=%s", channelID, userID))
+		}
+		return 0, errors.Wrapf(err, "failed to get lastViewedAt with channelId=%s and userId=%s", channelID, userID)
+	}
+
+	return lastViewedAt, nil
+}
+
 func (s SqlChannelStore) InvalidateAllChannelMembersForUser(userId string) {
 	allChannelMembersForUserCache.Remove(userId)
 	allChannelMembersForUserCache.Remove(userId + "_deleted")