mysql索引创建和使用细节(二)
自由TK 人气:0上篇粗略记录当mysql字段类型是string，传入int类型参数后失效当问题。
现在测试下mysql字段是int类型，传参string类型会发生什么。
题外话，最近膝盖手术后还在家养伤中，只怪自己以前骑车不注意休息保养，经常长途骑行出去玩，把膝盖骑费了(抽取积液+切除膝盖囊肿手术)，搞得现在哪都去不了，已经一周没下楼走走。
【索引失效】
二. 单字段索引：字段是INT类型，传入string类型参数
MySQL [test_db]> show create table test_users\G;
*************************** 1. row ***************************
Table: test_users
Create Table: CREATE TABLE `test_users` (
`uid` int(11) unsigned NOT NULL AUTO_INCREMENT,
`username` char(15) NOT NULL,
`created_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
`user_id` int(11) unsigned NOT NULL DEFAULT '0',
PRIMARY KEY (`uid`),
KEY `testindex` (`user_id`)
) ENGINE=InnoDB AUTO_INCREMENT=1306001 DEFAULT CHARSET=utf8mb4
1 row in set (0.05 sec)
ERROR: No query specified
#开启profile
MySQL [test_db]> set profiling =1;
Query OK, 0 rows affected, 1 warning (0.03 sec)
MySQL [test_db]> select * from test_users where user_id = '930324';
Empty set (0.03 sec)
MySQL [test_db]> select * from test_users where user_id = 899242;
Empty set (0.03 sec)
MySQL [test_db]> set profiling=0;
Query OK, 0 rows affected, 1 warning (0.04 sec)
MySQL [test_db]> show profiles; +----------+------------+---------------------------------------------------+ | Query_ID | Duration | Query | +----------+------------+---------------------------------------------------+ | 1 | 0.00034000 | select * from test_users where user_id = '930324' | | 2 | 0.00034850 | select * from test_users where user_id = 899242 | +----------+------------+---------------------------------------------------+ 2 rows in set, 1 warning (0.04 sec)
#可以看到两种查询耗时基本持平 MySQL [test_db]> explain select * from test_users where user_id = 899242; +----+-------------+------------+------------+------+---------------+-----------+---------+-------+------+----------+-------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+------------+------------+------+---------------+-----------+---------+-------+------+----------+-------+ | 1 | SIMPLE | test_users | NULL | ref | testindex | testindex | 4 | const | 1 | 100.00 | NULL | +----+-------------+------------+------------+------+---------------+-----------+---------+-------+------+----------+-------+ 1 row in set, 1 warning (0.03 sec) MySQL [test_db]> explain select * from test_users where user_id = '899242'; +----+-------------+------------+------------+------+---------------+-----------+---------+-------+------+----------+-------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+------------+------------+------+---------------+-----------+---------+-------+------+----------+-------+ | 1 | SIMPLE | test_users | NULL | ref | testindex | testindex | 4 | const | 1 | 100.00 | NULL | +----+-------------+------------+------------+------+---------------+-----------+---------+-------+------+----------+-------+ 1 row in set, 1 warning (0.04 sec) #再用explain分析下，可见两种查询都是key=testindex
上面针对的都是单字段索引，现在我们使用组合索引，对比下会有什么不一样。
三. 组合索引
MySQL [test_db]> show create table test_log\G;
*************************** 1. row ***************************
Table: test_log
Create Table: CREATE TABLE `test_log` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`log_id` int(11) unsigned NOT NULL DEFAULT '0',
`rand_name` char(15) NOT NULL,
`created_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
`country` varchar(50) NOT NULL DEFAULT '',
`short_country_name` char(5) NOT NULL DEFAULT '',
PRIMARY KEY (`id`),
KEY `c` (`country`),
KEY `log` (`log_id`,`rand_name`,`country`)
) ENGINE=InnoDB AUTO_INCREMENT=6601004 DEFAULT CHARSET=utf8mb4
1 row in set (0.04 sec)
ERROR: No query specified
MySQL [test_db]> set profiling=1;
Query OK, 0 rows affected, 1 warning (0.03 sec)
MySQL [test_db]> select * from test_log where log_id = '66423';
Empty set (0.04 sec)
MySQL [test_db]> select * from test_log where log_id = 987371;
+--------+--------+--------------+---------------------+--------------------+--------------------+
| id | log_id | rand_name | created_time | country | short_country_name |
+--------+--------+--------------+---------------------+--------------------+--------------------+
| 948373 | 987371 | 1ae53be9c1df | 2020-01-16 12:01:09 | 中国澳门特区 | MO |
+--------+--------+--------------+---------------------+--------------------+--------------------+
1 row in set (0.04 sec)
MySQL [test_db]> set profiling =0;
Query OK, 0 rows affected, 1 warning (0.03 sec)
MySQL [test_db]> show profiles;
+----------+------------+---------------------------------------------------+
| Query_ID | Duration | Query |
+----------+------------+---------------------------------------------------+
| 1 | 0.00034000 | select * from test_users where user_id = '930324' |
| 2 | 0.00034850 | select * from test_users where user_id = 899242 |
| 3 | 0.00464450 | select * from test_log where log_id = '66423' |
| 4 | 0.01399875 | select * from test_log where log_id = 987371 |
+----------+------------+---------------------------------------------------+
4 rows in set, 1 warning (0.03 sec)
#有没有发现什么不对劲的地方？
#没错 该组合索引里面 log_id是int类型，string类型参数比int类型参数快，到底哪里出问题？
#explain分析下
MySQL [test_db]> explain select * from test_log where log_id = '66423';
+----+-------------+----------+------------+------+---------------+------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+----------+------------+------+---------------+------+---------+-------+------+----------+-------+
| 1 | SIMPLE | test_log | NULL | ref | log | log | 4 | const | 1 | 100.00 | NULL |
+----+-------------+----------+------------+------+---------------+------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.05 sec)
MySQL [test_db]> explain select * from test_log where log_id = 987371;
+----+-------------+----------+------------+------+---------------+------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+----------+------------+------+---------------+------+---------+-------+------+----------+-------+
| 1 | SIMPLE | test_log | NULL | ref | log | log | 4 | const | 1 | 100.00 | NULL |
+----+-------------+----------+------------+------+---------------+------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.03 sec)
#explain得到的结果都是一模一样！！！ 而sql本身没什么区别只是一个查到数据一个没查到数据，那我再改下sql，让加单引号的能查到结果试试
MySQL [test_db]> set profiling = 1;
Query OK, 0 rows affected, 1 warning (0.03 sec)
MySQL [test_db]> select * from test_log where log_id = '3642103';
+---------+---------+--------------+---------------------+--------------------+--------------------+
| id | log_id | rand_name | created_time | country | short_country_name |
+---------+---------+--------------+---------------------+--------------------+--------------------+
| 3593106 | 3642103 | 37c0a4d8da6b | 2020-01-17 13:06:33 | 中国澳门特区 | MO |
+---------+---------+--------------+---------------------+--------------------+--------------------+
1 row in set (0.05 sec)
MySQL [test_db]> set profiling =0;
Query OK, 0 rows affected, 1 warning (0.03 sec)
MySQL [test_db]> show profiles;
+----------+------------+---------------------------------------------------+
| Query_ID | Duration | Query |
+----------+------------+---------------------------------------------------+
| 1 | 0.00034000 | select * from test_users where user_id = '930324' |
| 2 | 0.00034850 | select * from test_users where user_id = 899242 |
| 3 | 0.00464450 | select * from test_log where log_id = '66423' |
| 4 | 0.01399875 | select * from test_log where log_id = 987371 |
| 5 | 0.01888925 | select * from test_log where log_id = '3642103' |
+----------+------------+---------------------------------------------------+
5 rows in set, 1 warning (0.03 sec)
#耗时差别不大，我们猜测一下这里mysql默认将string类型转换成int类型了
#不相信的话，我们来验证下就知道了
MySQL [test_db]> select * from test_log where log_id = 'a666f';
Empty set (0.04 sec)
MySQL [test_db]> select * from test_log limit 1;
+----+--------+--------------+---------------------+--------------------------------+--------------------+
| id | log_id | rand_name | created_time | country | short_country_name |
+----+--------+--------------+---------------------+--------------------------------+--------------------+
| 1 | 1 | c4ca4238a0b9 | 2020-01-16 11:54:25 | 中立区(沙特-伊拉克间) | NT |
+----+--------+--------------+---------------------+--------------------------------+--------------------+
1 row in set (0.04 sec)
MySQL [test_db]> update test_log set log_id=0 where id = 1;
Query OK, 1 row affected (0.06 sec)
Rows matched: 1 Changed: 1 Warnings: 0
MySQL [test_db]> select * from test_log where log_id = 'a666f';
+----+--------+--------------+---------------------+--------------------------------+--------------------+
| id | log_id | rand_name | created_time | country | short_country_name |
+----+--------+--------------+---------------------+--------------------------------+--------------------+
| 1 | 0 | c4ca4238a0b9 | 2020-01-16 11:54:25 | 中立区(沙特-伊拉克间) | NT |
+----+--------+--------------+---------------------+--------------------------------+--------------------+
1 row in set (0.03 sec)
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