我有这个问题：
SELECT
s.last_spread, s.sd, s.mean, s.id
,c.id_ticker, c.coef
,t.ticker
,p.last, p.price
FROM (SELECT * FROM spreads WHERE spreads.id_check=1 LIMIT 100,500 ) as s
INNER JOIN coef as c
ON c.id_spread = s.id
INNER JOIN tickers AS t
ON t.id = c.id_ticker
LEFT JOIN (SELECT prices.id_ticker, MAX(prices.date) as last, prices.price FROM prices GROUP BY prices.id_ticker) AS p
ON p.id_ticker = t.id
这些是表格的模式：
mysql> desc spreads;
+-------------+---------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+---------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| id_check | int(11) | YES | MUL | NULL | |
| sd | double | YES | | NULL | |
| mean | double | YES | | NULL | |
| last_spread | double | YES | | NULL | |
+-------------+---------+------+-----+---------+----------------+
5 rows in set (0.00 sec)
mysql> desc coef;
+-----------+---------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+---------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| id_spread | int(11) | YES | MUL | NULL | |
| id_ticker | int(11) | YES | | NULL | |
| coef | double | YES | | NULL | |
| side | double | YES | | NULL | |
+-----------+---------+------+-----+---------+----------------+
5 rows in set (0.00 sec)
mysql> desc tickers;
+----------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| ticker | varchar(45) | NO | | NULL | |
| name | varchar(150) | NO | | NULL | |
| category | varchar(150) | NO | | NULL | |
| issuer | varchar(150) | NO | | NULL | |
+----------+------------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)
mysql> desc prices;
+-----------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| id_ticker | int(10) unsigned | NO | MUL | NULL | |
| date | date | NO | | NULL | |
| price | double | NO | | NULL | |
+-----------+------------------+------+-----+---------+----------------+
4 rows in set (0.01 sec)
这些是上表的索引;
mysql> show indexes from spreads;
+---------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+---------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| spreads | 0 | PRIMARY | 1 | id | A | 2299 | NULL | NULL | | BTREE | |
| spreads | 1 | check_idx | 1 | id_check | A | 1 | NULL | NULL | YES | BTREE | |
+---------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
2 rows in set (0.00 sec)
mysql> show indexes from coef;
+-------+------------+-------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-------+------------+-------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| coef | 0 | PRIMARY | 1 | id | A | 9078 | NULL | NULL | | BTREE | |
| coef | 1 | spread_ticker_idx | 1 | id_spread | A | NULL | NULL | NULL | YES | BTREE | |
| coef | 1 | spread_ticker_idx | 2 | id_ticker | A | NULL | NULL | NULL | YES | BTREE | |
+-------+------------+-------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
3 rows in set (0.00 sec)
mysql> show indexes from tickers;
+---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| tickers | 0 | PRIMARY | 1 | id | A | 100 | NULL | NULL | | BTREE | |
+---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
1 row in set (0.00 sec)
mysql> show indexes from prices;
+--------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+--------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| prices | 0 | PRIMARY | 1 | id | A | 19962 | NULL | NULL | | BTREE | |
| prices | 1 | id_ticker | 1 | id_ticker | A | 19962 | NULL | NULL | | BTREE | |
+--------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
2 rows in set (0.15 sec)
这是查询的解释：
+----+-------------+------------+--------+-------------------+-------------------+---------+---------------------------+--------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+------------+--------+-------------------+-------------------+---------+---------------------------+--------+-------------+
| 1 | PRIMARY | <derived2> | ALL | NULL | NULL | NULL | NULL | 500 | |
| 1 | PRIMARY | c | ref | spread_ticker_idx | spread_ticker_idx | 5 | s.id | 90 | Using where |
| 1 | PRIMARY | t | eq_ref | PRIMARY | PRIMARY | 4 | spreadtrading.c.id_ticker | 1 | Using where |
| 1 | PRIMARY | <derived3> | ALL | NULL | NULL | NULL | NULL | 100 | |
| 3 | DERIVED | prices | index | NULL | id_ticker | 4 | NULL | 119774 | |
| 2 | DERIVED | spreads | ref | check_idx | check_idx | 5 | | 2298 | Using where |
+----+-------------+------------+--------+-------------------+-------------------+---------+---------------------------+--------+-------------+
6 rows in set (0.27 sec)
我能优化吗？
谢谢！
修改
我想知道INDEXES和表的结构是否针对我上面发布的查询进行了优化。我使用此查询得到的结果很好，它运行良好，但也许我可以优化它以增加查询的“速度”。
答案 0 :(得分：0)
我认为你可以通过删除spreads子查询并将WHERE子句移到最后来获得一些东西，如下面的代码所示。这会失去你的LIMIT限制 - 也许你最后也可以放一个LIMIT条款，这取决于你在限制输出大小方面要达到的目的。
SELECT
s.last_spread, s.sd, s.mean, s.id
,c.id_ticker, c.coef
,t.ticker
,p.last, p.price
FROM spreads as s
INNER JOIN coef as c
ON c.id_spread = s.id
INNER JOIN tickers AS t
ON t.id = c.id_ticker
LEFT JOIN (SELECT prices.id_ticker, MAX(prices.date) as last, prices.price FROM prices GROUP BY prices.id_ticker) AS p
ON p.id_ticker = t.id
WHERE s.id_check = 1