如何解决如何在三个表40k行中优化缓慢的“选择不同的”查询，该查询仅返回22个结果
| 因此，我有一个我正在尝试重构的其他人编写的此查询，该查询为某项（通常是鞋子）提取了某些功能/材料。 有很多产品，因此有很多连接表项，但是只有少数几个功能可用。我在想，必须有一种方法来减少涉及“大”项目列表，获得这些功能的需要，而且我听说应避免使用明显的方法，但我不希望这样做。这里没有可以替换\“ distinct \”选项的声明。 根据我的日志，我得到的结果速度很慢： Query_time：7 Lock_time：0发送的行数：32已检查的行数：5362862 Query_time：8 Lock_time：0发送的行数：22已检查的行数：6581994 就像消息中说的那样，有时需要7或8秒，有时甚至每次要查询500万行以上。 这可能是由于同时发生其他负载，因为这是直接从mysql命令行在数据库上运行的选择：mysql> SELECT DISTINCT features.FeatureId,features.Name
FROM features,itemsfeatures,items
WHERE items.FlagStatus != \'U\'
AND items.TypeId = \'13\'
AND features.Type = \'Material\'
AND features.FeatureId = itemsfeatures.FeatureId
ORDER BY features.Name;
+-----------+--------------------+
| FeatureId | Name |
+-----------+--------------------+
| 40 | Alligator |
| 41 | Burnished Calfskin |
| 42 | Calfskin |
| 59 | Canvas |
| 43 | Chromexcel |
| 44 | Cordovan |
| 57 | Cotton |
| 45 | Crocodile |
| 58 | Deerskin |
| 61 | Eel |
| 46 | Italian Leather |
| 47 | Lizard |
| 48 | Nappa |
| 49 | NuBuck |
| 50 | Ostrich |
| 51 | Patent Leather |
| 60 | Rubber |
| 52 | Sharkskin |
| 53 | Silk |
| 54 | Suede |
| 56 | Veal |
| 55 | Woven |
+-----------+--------------------+
22 rows in set (0.00 sec)
mysql> select count(*) from features;
+----------+
| count(*) |
+----------+
| 122 |
+----------+
1 row in set (0.00 sec)
mysql> select count(*) from itemsfeatures;
+----------+
| count(*) |
+----------+
| 38569 |
+----------+
1 row in set (0.00 sec)
mysql> select count(*) from items;
+----------+
| count(*) |
+----------+
| 8656 |
+----------+
1 row in set (0.00 sec)
explain SELECT DISTINCT features.FeatureId,features.Name FROM features,items WHERE items.FlagStatus != \'U\' AND items.TypeId = \'13\' AND features.Type = \'Material\' AND features.FeatureId = itemsfeatures.FeatureId ORDER BY features.Name;
+----+-------------+---------------+------+-------------------+-----------+---------+---------------------------------+------+----------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+---------------+------+-------------------+-----------+---------+---------------------------------+------+----------------------------------------------+
| 1 | SIMPLE | features | ref | PRIMARY,Type | Type | 33 | const | 21 | Using where; Using temporary; Using filesort |
| 1 | SIMPLE | itemsfeatures | ref | FeatureId | FeatureId | 4 | sherman_live.features.FeatureId | 324 | Using index; Distinct |
| 1 | SIMPLE | items | ALL | TypeId,FlagStatus | NULL | NULL | NULL | 8656 | Using where; Distinct; Using join buffer |
+----+-------------+---------------+------+-------------------+-----------+---------+---------------------------------+------+----------------------------------------------+
3 rows in set (0.04 sec)
SELECT features.FeatureId,features.Name FROM features,items WHERE items.FlagStatus != \'U\' AND items.TypeId = \'13\' AND features.Type = \'Material\' AND features.FeatureId = itemsfeatures.FeatureId ORDER BY features.Name limit 10;
+-----------+-----------+
| FeatureId | Name |
+-----------+-----------+
| 40 | Alligator |
| 40 | Alligator |
| 40 | Alligator |
| 40 | Alligator |
| 40 | Alligator |
| 40 | Alligator |
| 40 | Alligator |
| 40 | Alligator |
| 40 | Alligator |
| 40 | Alligator |
+-----------+-----------+
10 rows in set (23.30 sec)
SELECT features.FeatureId,items WHERE items.FlagStatus != \'U\' AND items.TypeId = \'13\' AND features.Type = \'Material\' AND features.FeatureId = itemsfeatures.FeatureId group by features.name ORDER BY features.Name;
+-----------+--------------------+
| FeatureId | Name |
+-----------+--------------------+
| 40 | Alligator |
| 41 | Burnished Calfskin |
| 42 | Calfskin |
| 59 | Canvas |
| 43 | Chromexcel |
| 44 | Cordovan |
| 57 | Cotton |
| 45 | Crocodile |
| 58 | Deerskin |
| 61 | Eel |
| 46 | Italian Leather |
| 47 | Lizard |
| 48 | Nappa |
| 49 | NuBuck |
| 50 | Ostrich |
| 51 | Patent Leather |
| 60 | Rubber |
| 52 | Sharkskin |
| 53 | Silk |
| 54 | Suede |
| 56 | Veal |
| 55 | Woven |
+-----------+--------------------+
22 rows in set (13.28 sec)
解决方法
如Joe所述，似乎确实缺少联接条件
这是您当前的查询
SELECT DISTINCT
features.FeatureId,features.Name
FROM features,itemsfeatures,items
WHERE items.FlagStatus != \'U\'
AND items.TypeId = \'13\'
AND features.Type = \'Material\'
AND features.FeatureId = itemsfeatures.FeatureId
ORDER BY features.Name
SELECT DISTINCT
features.FeatureId,features.Name
FROM features INNER JOIN
itemsfeatures on features.FeatureId = itemsfeatures.FeatureId CROSS JOIN
items
WHERE items.FlagStatus != \'U\'
AND items.TypeId = \'13\'
AND features.Type = \'Material\'
ORDER BY features.Name
SELECT DISTINCT
features.FeatureId,itemsfeatures
WHERE features.Type = \'Material\'
AND features.FeatureId = itemsfeatures.FeatureId
ORDER BY features.Name
SELECT features.FeatureId,features.Name
FROM features INNER JOIN
itemsfeatures on features.FeatureId = itemsfeatures.FeatureId INNER JOIN
items on itemsfeatures.ItemID = items.ItemID
WHERE items.FlagStatus != \'U\'
AND items.TypeId = \'13\'
AND features.Type = \'Material\'
GROUP BY features.FeatureId,features.Name
ORDER BY features.Name
FeaturesIndex(Type,FeatureID,Name)
ItemsFeaturesIndex(FeatureId)
ItemsIndex(TypeId,FlagStatus,ItemID)
itemsfeatures
items
SELECT DISTINCT f.FeatureId,f.Name
FROM features f
INNER JOIN itemsfeatures ifx
ON f.FeatureID = ifx.FeatureID
INNER JOIN items i
ON ifx.ItemID = i.ItemID /* This is the part you\'re missing */
WHERE i.FlagStatus != \'U\'
AND i.TypeId = \'13\'
AND f.Type = \'Material\'
ORDER BY f.Name;
SELECT DISTINCT features.FeatureId,features.Name
FROM features,itemsfeatures
WHERE features.Type = \'Material\'
AND features.FeatureId = itemsfeatures.FeatureId
ORDER BY features.Name;
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