我有这个查询，加载时间太长（大约40秒）。
SELECT
`auxiliary_table_2`.`entry_id`,
`auxiliary_table_2`. `name`,
COUNT(`auxiliary_table_2`.`entry_id`) AS `auxiliary_table_2_count`
FROM (SELECT
`data_table`.*
FROM `data_table`
LEFT JOIN `exp_channels`
ON `exp_channels`.`channel_id` = `data_table`.`channel_id`
LEFT JOIN `exp_channel_titles`
ON `exp_channel_titles`.`entry_id` = `data_table`.`entry_id`
WHERE `exp_channels`.`channel_name` = 'main_table'
AND `exp_channel_titles`.`status` = 'open'
GROUP BY `data_table`.`entry_id`) AS `main_table`
JOIN `mapping_table` AS `mapping_table_1`
ON `mapping_table_1`.`rel_id` = `main_table`.`field_id_9`
JOIN (SELECT
`data_table`.`entry_id`,
`data_table`.`field_id_8` AS `name`
FROM `data_table`
LEFT JOIN `exp_channels`
ON `exp_channels`.`channel_id` = `data_table`.`channel_id`
WHERE `exp_channels`.`channel_name` = 'auxiliary_table_channel_name_1'
GROUP BY `data_table`.`entry_id`) AS `auxiliary_table_1`
ON `auxiliary_table_1`.`entry_id` = `mapping_table_1`.`rel_child_id`
JOIN `mapping_table` AS `mapping_table_2`
ON `mapping_table_2`.`rel_id` = `main_table`.`field_id_39`
JOIN (SELECT
`data_table`.`entry_id`,
`data_table`.`field_id_38` AS `name`
FROM `data_table`
LEFT JOIN `exp_channels`
ON `exp_channels`.`channel_id` = `data_table`.`channel_id`
WHERE `exp_channels`.`channel_name` = 'auxiliary_table_channel_name_2'
GROUP BY `data_table`.`entry_id`) AS `auxiliary_table_2`
ON `auxiliary_table_2`.`entry_id` = `mapping_table_2`.`rel_child_id`
JOIN `mapping_table` AS `mapping_table_3`
ON `mapping_table_3`.`rel_id` = `main_table`.`field_id_5`
JOIN (SELECT
`data_table`.`entry_id`,
`data_table`.`field_id_1` AS `name`
FROM `data_table`
LEFT JOIN `exp_channels`
ON `exp_channels`.`channel_id` = `data_table`.`channel_id`
WHERE `exp_channels`.`channel_name` = 'auxiliary_table_channel_name_3'
GROUP BY `data_table`.`entry_id`) AS `auxiliary_table_3`
ON `auxiliary_table_3`.`entry_id` = `mapping_table_3`.`rel_child_id`
JOIN `mapping_table` AS `mapping_table_4`
ON `mapping_table_4`.`rel_id` = `main_table`.`field_id_16`
JOIN (SELECT
`data_table`.`entry_id`,
`data_table`.`field_id_18` AS `name`
FROM `data_table`
LEFT JOIN `exp_channels`
ON `exp_channels`.`channel_id` = `data_table`.`channel_id`
WHERE `exp_channels`.`channel_name` = 'auxiliary_table_channel_name_4'
GROUP BY `data_table`.`entry_id`) AS `auxiliary_table_4`
ON `auxiliary_table_4`.`entry_id` = `mapping_table_4`.`rel_child_id`
JOIN `mapping_table` AS `mapping_table_5`
ON `mapping_table_5`.`rel_id` = `main_table`.`field_id_49`
JOIN (SELECT
`data_table`.`entry_id`,
`data_table`.`field_id_48` AS `name`
FROM `data_table`
LEFT JOIN `exp_channels`
ON `exp_channels`.`channel_id` = `data_table`.`channel_id`
WHERE `exp_channels`.`channel_name` = 'auxiliary_table_channel_name_5'
GROUP BY `data_table`.`entry_id`) AS `auxiliary_table_5`
ON `auxiliary_table_5`.`entry_id` = `mapping_table_5`.`rel_child_id`
GROUP BY `auxiliary_table_2`.`entry_id`
它的要点是data_table在辅助表中具有通过映射表映射的辅助数据。 main_table只是一个过滤后的数据表。
这里有什么东西可能导致它运行缓慢吗？
data_table只有少量行（大约200+）所以我认为这是一个查询问题。
这是EXPLAIN结果
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY <derived4> ALL NULL NULL NULL NULL 3 Using temporary; Using filesort
1 PRIMARY <derived6> ALL NULL NULL NULL NULL 5 Using join buffer
1 PRIMARY <derived7> ALL NULL NULL NULL NULL 6 Using join buffer
1 PRIMARY <derived3> ALL NULL NULL NULL NULL 21 Using join buffer
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 20 Using join buffer
1 PRIMARY <derived5> ALL NULL NULL NULL NULL 143 Using join buffer
1 PRIMARY auxiliary_table_1 eq_ref PRIMARY,rel_child_id PRIMARY 4 main_table.field_id_9 1 Using where
1 PRIMARY auxiliary_table_2 eq_ref PRIMARY,rel_child_id PRIMARY 4 main_table.field_id_39 1 Using where
1 PRIMARY auxiliary_table_3 eq_ref PRIMARY,rel_child_id PRIMARY 4 main_table.field_id_5 1 Using where
1 PRIMARY auxiliary_table_4 eq_ref PRIMARY,rel_child_id PRIMARY 4 main_table.field_id_16 1 Using where
1 PRIMARY auxiliary_table_5 eq_ref PRIMARY,rel_child_id PRIMARY 4 main_table.field_id_49 1 Using where
7 DERIVED exp_channels ref PRIMARY,channel_name channel_name 122 1 Using where; Using temporary; Using filesort
7 DERIVED exp_channel_data ref channel_id channel_id 4 devthree_ee.exp_channels.channel_id 17
6 DERIVED exp_channels ref PRIMARY,channel_name channel_name 122 1 Using where; Using temporary; Using filesort
6 DERIVED exp_channel_data ref channel_id channel_id 4 devthree_ee.exp_channels.channel_id 17
5 DERIVED exp_channels ref PRIMARY,channel_name channel_name 122 1 Using where; Using temporary; Using filesort
5 DERIVED exp_channel_data ref channel_id channel_id 4 devthree_ee.exp_channels.channel_id 17
4 DERIVED exp_channels ref PRIMARY,channel_name channel_name 122 1 Using where; Using temporary; Using filesort
4 DERIVED exp_channel_data ref channel_id channel_id 4 devthree_ee.exp_channels.channel_id 17
3 DERIVED exp_channels ref PRIMARY,channel_name channel_name 122 1 Using where; Using temporary; Using filesort
3 DERIVED exp_channel_data ref channel_id channel_id 4 devthree_ee.exp_channels.channel_id 17
2 DERIVED exp_channels ref PRIMARY,channel_name channel_name 122 1 Using where; Using temporary; Using filesort
2 DERIVED exp_channel_data ref PRIMARY,channel_id channel_id 4 devthree_ee.exp_channels.channel_id 17
2 DERIVED exp_channel_titles eq_ref PRIMARY,status PRIMARY 4 devthree_ee.exp_channel_data.entry_id 1 Using where
MYSQL VERSION：
我正在使用MySQL 5.1.66-cll
TABLES：
data_table
# Name Type Collation Attributes Null Default Extra
1 entry_id int(10) UNSIGNED No None
2 site_id int(4) UNSIGNED No 1
3 channel_id int(4) UNSIGNED No None
4 field_id_1 text utf8_general_ci Yes NULL
5 field_ft_1 tinytext utf8_general_ci Yes NULL
6 field_id_2 text utf8_general_ci Yes NULL
7 field_ft_2 tinytext utf8_general_ci Yes NULL
8 field_id_3 text utf8_general_ci Yes NULL
9 field_ft_3 tinytext utf8_general_ci Yes NULL
10 field_id_4 int(11) Yes 0
11 field_ft_4 tinytext utf8_general_ci Yes NULL
12 field_id_5 int(10) Yes 0
13 field_ft_5 tinytext utf8_general_ci Yes NULL
14 field_id_6 text utf8_general_ci Yes NULL
.....
mapping_table
# Name Type Collation Attributes Null Default Extra
1 rel_id int(6) UNSIGNED No None AUTO_INCREMENT
2 rel_parent_id int(10) No 0
3 rel_child_id int(10) No 0
4 rel_type varchar(12) utf8_general_ci No None
5 rel_data mediumtext utf8_general_ci No None
6 reverse_rel_data mediumtext utf8_general_ci No None
P.S。出于匿名目的，我已将表名替换为通用名称。