我在mysql查询中遇到以下问题：
SELECT t2.ordering, t1.family, t1.type, t1.game
FROM (SELECT
landbased_results.game,
landbased_results.type,
landbased_results.family
FROM landbased_results
Group by family, type,game) t1
LEFT JOIN
(SELECT family, ordering FROM family_order) t2
ON t1.family = t2.family
ORDER BY t2.ordering, t1.family, t1.type, t1.game ASC
给我以下结果：
+----------+--------------+-------------+---------+
| ordering | family | type | game |
+----------+--------------+-------------+---------+
| NULL | Punto Banco | Punto Banco | PB 1 |
| NULL | Punto Banco | Punto Banco | PB 2 |
| NULL | Punto Banco | Punto Banco | PB 3 |
| 1 | Roulette | Canasta | CA 1 |
| 1 | Roulette | Canasta | CA 2 |
| 1 | Roulette | Canasta | CA 3 |
| 1 | Roulette | Canasta | CA 4 |
| 2 | Blackjack | Rummy | RUM 1 |
| 2 | Blackjack | Rummy | RUM 2 |
| 2 | Blackjack | Rummy | RUM 3 |
| 2 | Blackjack | Rummy | RUM 4 |
| 2 | Blackjack | Rummy | RUM 5 |
| 4 | Multi-games | Multi-games | MULTI 1 |
| 4 | Multi-games | Multi-games | MULTI 2 |
| 4 | Multi-games | Multi-games | MULTI 3 |
| 5 | Pokers | Pai Go | PG 1 |
| 5 | Pokers | Pai Go | PG 2 |
| 5 | Pokers | Poker | PK 1 |
| 5 | Pokers | Texas | TEXAS 1 |
| 5 | Pokers | Texas | TEXAS 2 |
| 5 | Pokers | Texas | TEXAS 3 |
| 5 | Pokers | Tute | TUTE 1 |
| 7 | Craps | Craps | CR 1 |
| 8 | Slots | Slots | Slots |
+----------+--------------+-------------+---------+
为什么我在＆＃34;订购＆＃34;？中得到一个NULL结果？该表有一个明确的订购密钥：
+----+-------------+----------+
| id | family | ordering |
+----+-------------+----------+
| 1 | Blackjack | 2 |
| 2 | Craps | 7 |
| 3 | Multi-games | 4 |
| 4 | Pokers | 5 |
| 5 | Punto Banco | 3 |
| 6 | Roulette | 1 |
| 7 | Slots | 8 |
| 8 | Super Pic | 6 |
+----+-------------+----------+
我做错了什么？