mysql索引创建和使用细节(二)
2024-10-08 06:45:59
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 '',
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 = '';
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 = '' |
| 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 = '';
+----+-------------+------------+------------+------+---------------+-----------+---------+-------+------+----------+-------+
| 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 '',
`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 = '';
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 = '' |
| 2 | 0.00034850 | select * from test_users where user_id = 899242 |
| 3 | 0.00464450 | select * from test_log where log_id = '' |
| 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 = '';
+----+-------------+----------+------------+------+---------------+------+---------+-------+------+----------+-------+
| 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！！！ 那为什么有快慢之分，为了方便数据比较，我们重连mysql连接l。 Database changed
MySQL [test_db]> set profiling = 1;
Query OK, 0 rows affected, 1 warning (0.04 sec) MySQL [test_db]> select * from test_log where log_id = '';
+---------+---------+--------------+---------------------+--------------------+--------------------+
| id | log_id | rand_name | created_time | country | short_country_name |
+---------+---------+--------------+---------------------+--------------------+--------------------+
| 5941183 | 5990180 | 970eb4c2f8e8 | 2020-01-17 13:20:37 | 吉尔吉斯斯坦 | KG |
+---------+---------+--------------+---------------------+--------------------+--------------------+
1 row in set (0.05 sec) MySQL [test_db]> select * from test_log where log_id = '';
+---------+---------+--------------+---------------------+-----------------+--------------------+
| id | log_id | rand_name | created_time | country | short_country_name |
+---------+---------+--------------+---------------------+-----------------+--------------------+
| 2950083 | 2999080 | 805c2b1fbab1 | 2020-01-17 13:02:40 | 所罗门群岛 | Sb |
+---------+---------+--------------+---------------------+-----------------+--------------------+
1 row in set (0.03 sec) MySQL [test_db]> select * from test_log where log_id = '';
+---------+---------+--------------+---------------------+-----------+--------------------+
| id | log_id | rand_name | created_time | country | short_country_name |
+---------+---------+--------------+---------------------+-----------+--------------------+
| 3851245 | 3900242 | f19fcdd1172e | 2020-01-17 13:08:21 | 菲律宾 | PH |
+---------+---------+--------------+---------------------+-----------+--------------------+
1 row in set (0.03 sec) MySQL [test_db]> select * from test_log where log_id = '';
+---------+---------+--------------+---------------------+--------------------------------+--------------------+
| id | log_id | rand_name | created_time | country | short_country_name |
+---------+---------+--------------+---------------------+--------------------------------+--------------------+
| 4391245 | 4440242 | fd03f30dfc3e | 2020-01-17 13:11:20 | 圣文森特和格陵纳丁斯 | VC |
+---------+---------+--------------+---------------------+--------------------------------+--------------------+
1 row in set (0.04 sec) MySQL [test_db]> select * from test_log where log_id = 23440242;
Empty set (0.03 sec) MySQL [test_db]> select * from test_log where log_id = 2344042;
+---------+---------+--------------+---------------------+--------------+--------------------+
| id | log_id | rand_name | created_time | country | short_country_name |
+---------+---------+--------------+---------------------+--------------+--------------------+
| 2295045 | 2344042 | bc89598c0d10 | 2020-01-17 12:58:47 | 格鲁吉亚 | GE |
+---------+---------+--------------+---------------------+--------------+--------------------+
1 row in set (0.03 sec) MySQL [test_db]> select * from test_log where log_id = 5314042;
+---------+---------+--------------+---------------------+--------------------------+--------------------+
| id | log_id | rand_name | created_time | country | short_country_name |
+---------+---------+--------------+---------------------+--------------------------+--------------------+
| 5265045 | 5314042 | 452e5ecf5fa5 | 2020-01-17 13:16:44 | 特立尼达和多巴哥 | TT |
+---------+---------+--------------+---------------------+--------------------------+--------------------+
1 row in set (0.03 sec) MySQL [test_db]> select * from test_log where log_id = 5614092;
+---------+---------+--------------+---------------------+--------------+--------------------+
| id | log_id | rand_name | created_time | country | short_country_name |
+---------+---------+--------------+---------------------+--------------+--------------------+
| 5565095 | 5614092 | 78adae2b40a3 | 2020-01-17 13:18:31 | 马约特岛 | YT |
+---------+---------+--------------+---------------------+--------------+--------------------+
1 row in set (0.03 sec) MySQL [test_db]> select * from test_log where log_id = 5900392;
+---------+---------+--------------+---------------------+---------+--------------------+
| id | log_id | rand_name | created_time | country | short_country_name |
+---------+---------+--------------+---------------------+---------+--------------------+
| 5851395 | 5900392 | e89ccadae397 | 2020-01-17 13:20:19 | 挪威 | NO |
+---------+---------+--------------+---------------------+---------+--------------------+
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 | 0.01717650 | select * from test_log where log_id = '' |
| 2 | 0.00281950 | select * from test_log where log_id = '' |
| 3 | 0.00167475 | select * from test_log where log_id = '' |
| 4 | 0.00431675 | select * from test_log where log_id = '' |
| 5 | 0.00032000 | select * from test_log where log_id = 23440242 |
| 6 | 0.00387325 | select * from test_log where log_id = 2344042 |
| 7 | 0.00461725 | select * from test_log where log_id = 5314042 |
| 8 | 0.00485450 | select * from test_log where log_id = 5614092 |
| 9 | 0.00476200 | select * from test_log where log_id = 5900392 |
+----------+------------+-------------------------------------------------+
9 rows in set, 1 warning (0.04 sec)
#通过对比发现字段为int类型是，参数是int还是string对耗时影响不大
#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) MySQL [test_db]> select * from test_log where log_id = '12a1a';
+----+--------+--------------+---------------------+---------+--------------------+
| id | log_id | rand_name | created_time | country | short_country_name |
+----+--------+--------------+---------------------+---------+--------------------+
| 12 | 12 | c20ad4d76fe9 | 2020-01-16 11:54:25 | 英国 | UK |
+----+--------+--------------+---------------------+---------+--------------------+
1 row in set (0.04 sec) MySQL [test_db]> select * from test_log where log_id = '02a1a';
+----+--------+--------------+---------------------+---------+--------------------+
| id | log_id | rand_name | created_time | country | short_country_name |
+----+--------+--------------+---------------------+---------+--------------------+
| 2 | 2 | c81e728d9d4c | 2020-01-16 11:54:25 | 中国 | CN |
+----+--------+--------------+---------------------+---------+--------------------+
1 row in set (0.03 sec)
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