mysql索引创建和使用细节(二)

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！！！ 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 = ‘5990180‘;
+---------+---------+--------------+---------------------+--------------------+--------------------+
| 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 = ‘2999080‘;
+---------+---------+--------------+---------------------+-----------------+--------------------+
| 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 = ‘3900242‘;
+---------+---------+--------------+---------------------+-----------+--------------------+
| 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 = ‘4440242‘;
+---------+---------+--------------+---------------------+--------------------------------+--------------------+
| 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 = ‘5990180‘ |
|        2 | 0.00281950 | select * from test_log where log_id = ‘2999080‘ |
|        3 | 0.00167475 | select * from test_log where log_id = ‘3900242‘ |
|        4 | 0.00431675 | select * from test_log where log_id = ‘4440242‘ |
|        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)

原文地址：https://www.cnblogs.com/wscsq789/p/12208725.html

时间： 2024-10-11 05:02:13

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