how to speed up the mysql query to count average value? - mysql

Question

the table structure is follow:
CREATE TABLE `crm_member` (
`member_id` int(11) NOT NULL AUTO_INCREMENT,
`shop_id` int(11) NOT NULL,
`nick` varchar(255) NOT NULL DEFAULT '',
`name` varchar(255) NOT NULL DEFAULT '',
`mobile` varchar(255) NOT NULL DEFAULT '',
`grade` int(11) NOT NULL DEFAULT '-1',
`trade_count` int(11) NOT NULL,
`trade_amount` float NOT NULL,
`last_trade_time` int(11) NOT NULL,
`trade_from` tinyint(4) NOT NULL,
`avg_price` float NOT NULL,
`seller_flag` tinyint(1) NOT NULL,
`is_black` tinyint(1) NOT NULL DEFAULT '0',
`created` int(11) NOT NULL,
PRIMARY KEY (`member_id`),
UNIQUE KEY `shop_id` (`shop_id`,`nick`),
KEY `last_trade_time` (`last_trade_time`),
KEY `idx_shop_id_grade` (`shop_id`,`grade`),
KEY `idx_shopid_created` (`shop_id`,`created`),
KEY `idx_trade_amount` (`shop_id`,`trade_amount`),
KEY `idx_trade_count` (`shop_id`,`trade_count`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
the table has 2148037 rows under the shop_id 3498706;
AND my query is like
SELECT AVG(trade_count) as trade_count, AVG(trade_amount) as trade_amount, AVG(grade) as grade from `crm_member_0141` WHERE shop_id = '3498706' and grade >= 0 and trade_count > 0 and is_black = 0 LIMIT 1
the query exec about 30 seconds .
the explain result
mysql> explain SELECT member_id, AVG(trade_count) as trade_count, AVG(trade_amount) as trade_amount, AVG(grade) as grade from `crm_member_0141` WHERE shop_id = 3498706 and grade >= 0 and trade_count > 0 and is_black = 0 order by member_id LIMIT 1;
+----+-------------+-----------------+------------+------+-------------------------------------------------------------------------------+---------+---------+-------+---------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-----------------+------------+------+-------------------------------------------------------------------------------+---------+---------+-------+---------+----------+-------------+
| 1 | SIMPLE | crm_member_0141 | NULL | ref | shop_id,idx_shop_id_grade,idx_shopid_created,idx_trade_amount,idx_trade_count | shop_id | 4 | const | 1074018 | 1.11 | Using where |
+----+-------------+-----------------+------------+------+-------------------------------------------------------------------------------+---------+---------+-------+---------+----------+-------------+
how to speed up the query?

Answer 1

It looks like mysql chooses to use the primary key instead of the shop_id, grade index, although shop_id, grade would probably speed up the selection of rows.
You can tell mysql to use a specific index for a query, using the USE INDEX directive :
try to add USE INDEX (idx_shop_id_grade) in your query after the table name and see if the computation is faster.
Otherwise, if this query is especially useful and frequent to call in your app, you can build a more specialised index for this query :
Your query selects on a particular value for shop_id and is_black, then does a range selection on grade and trade_count.
I would suggest to try indexing using shop_id, is_black, grade, trade_count.
note : obviously, test this first on test database