무료 추천: mysql 동영상 튜토리얼
create table t_index( id int not null auto_increment, title varchar(30) not null default '', email varchar(30) not null default '', primary key(id), unique key uni_email(email) , key key_title(title) )engine=innodb charset=utf8;
View table
desc tablename
mysql> desc t_index; +-------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | title | varchar(30) | NO | MUL | | | | email | varchar(30) | NO | UNI | | | +-------+-------------+------+-----+---------+----------------+ 3 rows in set (0.01 sec)
desc tablenamemysql> show create table t_index/G; ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '/G' at line 1 mysql> show create table t_index\G; *************************** 1. row *************************** Table: t_index Create Table: CREATE TABLE `t_index` ( `id` int(11) NOT NULL AUTO_INCREMENT, `title` varchar(30) NOT NULL DEFAULT '', `email` varchar(30) NOT NULL DEFAULT '', PRIMARY KEY (`id`), UNIQUE KEY `uni_email` (`email`), KEY `key_title` (`title`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 1 row in set (0.00 sec) ERROR: No query specified
查看表的创建语句
show create table tbalename/G
mysql> alter table t_index drop primary key; ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key
alter table table_name drop primary key;
注意：
mysql> alter table t_index modify id int not null; Query OK, 0 rows affected (0.05 sec) Records: 0 Duplicates: 0 Warnings: 0
主键不一定是自增长，但是自增长一定是主键。
删除逐渐之前先要把主键索引的自增长去掉。
mysql> alter table t_index drop primary key; Query OK, 0 rows affected (0.04 sec) Records: 0 Duplicates: 0 Warnings: 0
再来删除主键
mysql> alter table t_index drop key uni_email; Query OK, 0 rows affected (0.03 sec) Records: 0 Duplicates: 0 Warnings: 0
alter table table_name drop key ‘索引的别名’
实际操作
mysql> alter table t_index drop key key_title; Query OK, 0 rows affected (0.02 sec) Records: 0 Duplicates: 0 Warnings: 0
alter table t_index add key key_title(title); alter table t_index add key uni_email(email); alter table t_index add primary key(id);
create table article( id int not null auto_increment, no_index int, title varchar(30) not null default '', add_time datetime, primary key(id) );
mysql> insert into article(id,title,add_time) values(null,'ddsd1212123d',now()); mysql> insert into article(title,add_time) select title,now() from article; Query OK, 10 rows affected (0.01 sec) Records: 10 Duplicates: 0 Warnings: 0 mysql> update article set no_index=id;
插入数据
mysql> select * from article where no_index=1495298; +---------+----------+-----------+---------------------+ | id | no_index | title | add_time | +---------+----------+-----------+---------------------+ | 1495298 | 1495298 | ddsd1123d | 2019-05-15 23:13:56 | +---------+----------+-----------+---------------------+ 1 row in set (0.28 sec)
有无索引查询数据对比
mysql> select * from article where id=1495298; +---------+----------+-----------+---------------------+ | id | no_index | title | add_time | +---------+----------+-----------+---------------------+ | 1495298 | 1495298 | ddsd1123d | 2019-05-15 23:13:56 | +---------+----------+-----------+---------------------+ 1 row in set (0.01 sec)
mysql> show create table article\G; *************************** 1. row *************************** Table: article Create Table: CREATE TABLE `article` ( `id` int(11) NOT NULL AUTO_INCREMENT, `no_index` int(11) DEFAULT NULL, `title` varchar(30) NOT NULL DEFAULT '', `add_time` datetime DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=1572824 DEFAULT CHARSET=utf8 1 row in set (0.00 sec) ERROR: No query specified
表结构
mysql> mysql> explain select * from article where no_index=1495298\G; *************************** 1. row *************************** id: 1 select_type: SIMPLE//单表查询 table: article//查询的表名 partitions: NULL type: ALL//索引的类型，从好到坏的情况是：system>const>range>index>All possible_keys: NULL//可能使用到的索引 key: NULL//实际使用到的索引 key_len: NULL//索引的长度 ref: NULL rows: 1307580//可能进行扫描表的行数 filtered: 10.00 Extra: Using where 1 row in set, 1 warning (0.00 sec) ERROR: No query specified
使用explain可以对sql语句进行分析到底有没有使用到索引查询,从而更好的优化它.
我们只需要在select语句前面加上一句explain或者desc.
explain|desc select * from tablename G;
show create table tbalename/ G
mysql> explain select * from article where id=1495298\G; *************************** 1. row *************************** id: 1 select_type: SIMPLE table: article partitions: NULL type: const//当对主键索引进行等值查询的时候出现const possible_keys: PRIMARY key: PRIMARY//实际使用到的所有primary索引 key_len: 4//索引的长度4 = int占4个字节 ref: const rows: 1//所扫描的行数只有一行 filtered: 100.00 Extra: NULL 1 row in set, 1 warning (0.00 sec) ERROR: No query specified
기본 키 인덱스 삭제
alter table table_name drop 기본 키;mysql> use mysql; mysql> explain select * from user\G; *************************** 1. row *************************** id: 1 select_type: SIMPLE table: user partitions: NULL type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 3 filtered: 100.00 Extra: NULL 1 row in set, 1 warning (0.00 sec)
mysql> use test; mysql> explain select * from article where id=666666\G; *************************** 1. row *************************** id: 1 select_type: SIMPLE table: article partitions: NULL type: const possible_keys: PRIMARY key: PRIMARY key_len: 4 ref: const rows: 1 filtered: 100.00 Extra: NULL
mysql> explain select * from article where id>666666\G; mysql> explain select * from article where id<666666\G;
alter table table_name drop key '인덱스 별칭'mysql> explain select id from article \G; *************************** 1. row *************************** id: 1 select_type: SIMPLE table: article partitions: NULL type: index possible_keys: NULL key: PRIMARY key_len: 4 ref: NULL rows: 1307580 filtered: 100.00 Extra: Using index 1 row in set, 1 warning (0.00 sec) ERROR: No query specified
mysql> alter table article add key key_no_index(no_index); Query OK, 0 rows affected (1.92 sec) Records: 0 Duplicates: 0 Warnings: 0 type为ref，应该是关联，但是ref是const mysql> explain select * from article where no_index=666666\G; *************************** 1. row *************************** id: 1 select_type: SIMPLE table: article partitions: NULL type: ref possible_keys: key_no_index key: key_no_index key_len: 5 ref: const rows: 1 filtered: 100.00 Extra: NULL 1 row in set, 1 warning (0.00 sec) 速度飞跃 mysql> select * from article where no_index=666666; +--------+----------+-----------+---------------------+ | id | no_index | title | add_time | +--------+----------+-----------+---------------------+ | 666666 | 666666 | ddsd1123d | 2019-05-15 23:13:55 | +--------+----------+-----------+---------------------+ 1 row in set (0.00 sec)
3.
mysql> explain select * from article order by id\G; *************************** 1. row *************************** id: 1 select_type: SIMPLE table: article partitions: NULL type: index possible_keys: NULL key: PRIMARY key_len: 4 ref: NULL rows: 1307580 filtered: 100.00 Extra: NULL 1 row in set, 1 warning (0.00 sec) ERROR: No query specified mysql> explain select * from article where id >0 order by id\G; *************************** 1. row *************************** id: 1 select_type: SIMPLE table: article partitions: NULL type: range possible_keys: PRIMARY key: PRIMARY key_len: 4 ref: NULL rows: 653790 filtered: 100.00 Extra: Using where 1 row in set, 1 warning (0.01 sec) ERROR: No query specified
4. 인덱스가 있는 것과 없는 것의 비교
mysql> alter table article add key key_index(title); Query OK, 0 rows affected (2.16 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> show create table article\G; *************************** 1. row *************************** Table: article Create Table: CREATE TABLE `article` ( `id` int(11) NOT NULL AUTO_INCREMENT, `no_index` int(11) DEFAULT NULL, `title` varchar(30) NOT NULL DEFAULT '', `add_time` datetime DEFAULT NULL, PRIMARY KEY (`id`), KEY `key_no_index` (`no_index`), KEY `key_index` (`title`) ) ENGINE=InnoDB AUTO_INCREMENT=1507299 DEFAULT CHARSET=utf8 1 row in set (0.00 sec)
데이터 삽입
mysql> explain select * from article where title like 'a%'\G; *************************** 1. row *************************** id: 1 select_type: SIMPLE table: article partitions: NULL type: range//范围查询 possible_keys: key_index key: key_index key_len: 92// ref: NULL rows: 1 filtered: 100.00 Extra: Using index condition 1 row in set, 1 warning (0.00 sec) mysql> explain select * from article where title like '%a%'\G; *************************** 1. row *************************** id: 1 select_type: SIMPLE table: article partitions: NULL type: ALL//全表查询 possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 1307580 filtered: 11.11 Extra: Using where 1 row in set, 1 warning (0.00 sec)
인덱스가 있는 것과 없는 쿼리 데이터의 비교
mysql> explain select sql_no_cache * from article limit 90000,10 \G; *************************** 1. row *************************** id: 1 select_type: SIMPLE table: article partitions: NULL type: ALL//全表 possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 1307580 filtered: 100.00 Extra: NULL 1 row in set, 2 warnings (0.00 sec) ERROR: No query specified mysql> explain select sql_no_cache * from article order by id limit 90000,10 \G; *************************** 1. row *************************** id: 1 select_type: SIMPLE table: article partitions: NULL type: index possible_keys: NULL key: PRIMARY//使用到了索引 key_len: 4 ref: NULL rows: 90010 filtered: 100.00 Extra: NULL 1 row in set, 2 warnings (0.00 sec) ERROR: No query specified
mysql> select sql_no_cache * from article limit 1000000,10; +---------+----------+----------------+---------------------+ | id | no_index | title | add_time | +---------+----------+----------------+---------------------+ | 1196579 | 1196579 | ddsd12123123ad | 2019-05-15 23:13:56 | | 1196580 | 1196580 | ddsd121231ad | 2019-05-15 23:13:56 | | 1196581 | 1196581 | ddsd1212123d | 2019-05-15 23:13:56 | | 1196582 | 1196582 | ddsd1123123d | 2019-05-15 23:13:56 | | 1196583 | 1196583 | ddsd1123d | 2019-05-15 23:13:56 | | 1196584 | 1196584 | ddsd1123d | 2019-05-15 23:13:56 | | 1196585 | 1196585 | ddsd1123d | 2019-05-15 23:13:56 | | 1196586 | 1196586 | ddsd1123d | 2019-05-15 23:13:56 | | 1196587 | 1196587 | ddsd1123d | 2019-05-15 23:13:56 | | 1196588 | 1196588 | ddsd1123d | 2019-05-15 23:13:56 | +---------+----------+----------------+---------------------+ 10 rows in set, 1 warning (0.21 sec) mysql> select t1.* from article as t1 inner join (select id as pid from article limit 10000,10) as t2 on t1.id=t2.pid; +-------+----------+----------------+---------------------+ | id | no_index | title | add_time | +-------+----------+----------------+---------------------+ | 13058 | 13058 | ddsd12123123ad | 2019-05-15 23:13:49 | | 13059 | 13059 | ddsd121231ad | 2019-05-15 23:13:49 | | 13060 | 13060 | ddsd1212123d | 2019-05-15 23:13:49 | | 13061 | 13061 | ddsd1123123d | 2019-05-15 23:13:49 | | 13062 | 13062 | ddsd1123d | 2019-05-15 23:13:49 | | 13063 | 13063 | ddsd1123d | 2019-05-15 23:13:49 | | 13064 | 13064 | ddsd1123d | 2019-05-15 23:13:49 | | 13065 | 13065 | ddsd1123d | 2019-05-15 23:13:49 | | 13066 | 13066 | ddsd1123d | 2019-05-15 23:13:49 | | 13067 | 13067 | ddsd1123d | 2019-05-15 23:13:49 | +-------+----------+----------------+---------------------+ 10 rows in set (0.00 sec)
//给no_index和title创建一个复合索引 mysql> alter table article add key index_no_index_title(no_index,title); Query OK, 0 rows affected (1.18 sec) Records: 0 Duplicates: 0 Warnings: 0 //查看创建后的结构 mysql> show create table article\G; *************************** 1. row *************************** Table: article Create Table: CREATE TABLE `article` ( `id` int(11) NOT NULL AUTO_INCREMENT, `no_index` int(11) DEFAULT NULL, `title` varchar(30) NOT NULL DEFAULT '', `add_time` datetime DEFAULT NULL, PRIMARY KEY (`id`), KEY `key_no_index` (`no_index`), KEY `key_index` (`title`), KEY `index_no_index_title` (`no_index`,`title`) ) ENGINE=InnoDB AUTO_INCREMENT=1507299 DEFAULT CHARSET=utf8 1 row in set (0.00 sec) //删除no_index和title的索引 mysql> alter table article drop key key_index; Query OK, 0 rows affected (0.05 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> alter table article drop key key_no_index; Query OK, 0 rows affected (0.03 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> show create table article\G; *************************** 1. row *************************** Table: article Create Table: CREATE TABLE `article` ( `id` int(11) NOT NULL AUTO_INCREMENT, `no_index` int(11) DEFAULT NULL, `title` varchar(30) NOT NULL DEFAULT '', `add_time` datetime DEFAULT NULL, PRIMARY KEY (`id`), KEY `index_no_index_title` (`no_index`,`title`) ) ENGINE=InnoDB AUTO_INCREMENT=1507299 DEFAULT CHARSET=utf8 1 row in set (0.00 sec) //复合索引使用情况 mysql> explain select * from article where title='ddsd1123d' and no_index=77777\G; *************************** 1. row *************************** id: 1 select_type: SIMPLE table: article partitions: NULL type: ref possible_keys: index_no_index_title key: index_no_index_title key_len: 97 ref: const,const rows: 1 filtered: 100.00 Extra: NULL 1 row in set, 1 warning (0.00 sec) mysql> explain select * from article where no_index=77777\G; *************************** 1. row *************************** id: 1 select_type: SIMPLE table: article partitions: NULL type: ref possible_keys: index_no_index_title key: index_no_index_title key_len: 5 ref: const rows: 1 filtered: 100.00 Extra: NULL 1 row in set, 1 warning (0.00 sec)
explain을 사용하세요. 더 나은 최적화를 위해 인덱스 쿼리에 사용되거나 사용되지 않습니다.select 문 앞에 explain 또는 desc만 추가하면 됩니다.
1. Syntaxexplain|desc select * from tablename G;
지금 두 인덱스를 사용하여 비교하고 확인하세요mysql> show variables like '%slow_query%';
+---------------------+--------------------------------------------------+
| Variable_name | Value |
+---------------------+--------------------------------------------------+
| slow_query_log | OFF |
| slow_query_log_file | /usr/local/mysql/data/caredeMacBook-Pro-slow.log |
+---------------------+--------------------------------------------------+
2 rows in set (0.00 sec)
mysql> set global slow_query_log=on;
Query OK, 0 rows affected (0.00 sec)
유형 항목 분석은 최고에서 최악으로 정렬됩니다.
system: 일반 시스템 테이블 레코드 행이 하나만 있는 경우에만 나타납니다.
const: id=666666과 같이 기본 키 값에 대해 동일한 값 쿼리를 수행할 때 나타납니다. range
: 인덱스 값에 대해 범위 쿼리를 수행할 때 나타납니다. 예를 들어 where id<100000index
: 쿼리한 필드가 인덱스 파일의 값일 때 나타납니다.All: 피해야 할 최악의 상황
실제 테스트
mysql> show variables like '%slow_query%'; +---------------------+--------------------------------------------------+ | Variable_name | Value | +---------------------+--------------------------------------------------+ | slow_query_log | ON | | slow_query_log_file | /usr/local/mysql/data/caredeMacBook-Pro-slow.log | +---------------------+--------------------------------------------------+ 2 rows in set (0.00 sec)<div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">//查看profile设置 mysql> show variables like '%profil%'; +------------------------+-------+ | Variable_name | Value | +------------------------+-------+ | have_profiling | YES | | profiling | OFF |//未开启状态 | profiling_history_size | 15 | +------------------------+-------+ 3 rows in set (0.00 sec) //开启操作 mysql> set profiling = on; Query OK, 0 rows affected, 1 warning (0.00 sec) //查看是否开启成功 mysql> show variables like '%profil%'; +------------------------+-------+ | Variable_name | Value | +------------------------+-------+ | have_profiling | YES | | profiling | ON |//开启成功 | profiling_history_size | 15 | +------------------------+-------+ 3 rows in set (0.00 sec)
mysql> select * from article where no_index=666666; +--------+----------+-----------+---------------------+ | id | no_index | title | add_time | +--------+----------+-----------+---------------------+ | 666666 | 666666 | ddsd1123d | 2019-05-15 23:13:55 | +--------+----------+-----------+---------------------+ 1 row in set (0.02 sec) mysql> show profiles; +----------+------------+---------------------------------------------+ | Query_ID | Duration | Query | +----------+------------+---------------------------------------------+ | 1 | 0.00150700 | show variables like '%profil%' | | 2 | 0.01481100 | select * from article where no_index=666666 | +----------+------------+---------------------------------------------+ 2 rows in set, 1 warning (0.00 sec) mysql> show profile for query 2; +----------------------+----------+ | Status | Duration | +----------------------+----------+ | starting | 0.000291 | | checking permissions | 0.000007 | | Opening tables | 0.012663 |//打开表 | init | 0.000050 | | System lock | 0.000009 | | optimizing | 0.000053 | | statistics | 0.001566 | | preparing | 0.000015 | | executing | 0.000002 | | Sending data | 0.000091 |//磁盘上的发送数据 | end | 0.000004 | | query end | 0.000007 | | closing tables | 0.000006 | | freeing items | 0.000037 | | cleaning up | 0.000010 | +----------------------+----------+ 15 rows in set, 1 warning (0.01 sec)
쿼리된 필드가 인덱스 파일에 있으면 쿼리는 인덱스 파일에서 직접 수행됩니다. 인덱스 커버리지 쿼리.
모두 필드에 일반 인덱스 쿼리를 추가할 수 있습니다
rrreee4. 인덱스 사용 시나리오
🎜1 where 뒤에 자주 나타나는 필드의 경우 해당 필드에 인덱스를 추가해야 합니다🎜🎜2. order by 문 인덱스 최적화🎜rrreee🎜🎜인덱스를 사용해도 거의 풀테이블 스캔인 것을 알 수 있다. 🎜🎜🎜🎜where를 추가하면 절반으로 줄어듭니다🎜🎜🎜3. like🎜🎜🎜'%keyword%'와 같은 where 제목에 대한 퍼지 쿼리 인덱스 최적화 ====>전체 테이블 스캔🎜🎜🎜 🎜'키워드%'와 같은 제목 ===> 인덱스 쿼리가 사용됩니다🎜🎜🎜제목에 인덱스 추가🎜rrreee🎜🎜좋아요 키워드 쿼리의 가장 왼쪽에는 %가 표시되지 않으므로 인덱스 쿼리를 사용할 수 있습니다🎜 🎜🎜 🎜like 왼쪽에 %가 표시되는 한 전체 테이블 쿼리입니다🎜🎜rrreee🎜4. 제한문의 인덱스 사용 최적화🎜🎜제한문의 최적화를 위해 다음을 추가할 수 있습니다. order by index 필드가 앞에 있는 경우🎜🎜order by 필드가 인덱스이고 지정된 수의 데이터 행이 인덱스 파일에서 먼저 검색됩니다🎜rrreee🎜🎜한도에 대한 또 다른 최적화 방법:🎜🎜🎜인덱스 범위 + 지연 연관🎜🎜원리: 주로 인덱스 커버리지를 사용하여 쿼리합니다. 커버링 인덱스 쿼리에서 반환된 ID는 쿼리하려는 레코드의 ID와 연결됩니다. 🎜rrreee🎜5 가장 왼쪽의 복합 원칙(다중 열). index (인터뷰에서 자주 묻는 질문) 🎜🎜쿼리 중에 복합 인덱스의 가장 왼쪽 부분이 나타나면 기사 테이블의 필드만 인덱스 쿼리에 사용됩니다🎜🎜no_index와 기사 테이블 제목에 복합 인덱스를 생성합니다 :🎜//给no_index和title创建一个复合索引 mysql> alter table article add key index_no_index_title(no_index,title); Query OK, 0 rows affected (1.18 sec) Records: 0 Duplicates: 0 Warnings: 0 //查看创建后的结构 mysql> show create table article\G; *************************** 1. row *************************** Table: article Create Table: CREATE TABLE `article` ( `id` int(11) NOT NULL AUTO_INCREMENT, `no_index` int(11) DEFAULT NULL, `title` varchar(30) NOT NULL DEFAULT '', `add_time` datetime DEFAULT NULL, PRIMARY KEY (`id`), KEY `key_no_index` (`no_index`), KEY `key_index` (`title`), KEY `index_no_index_title` (`no_index`,`title`) ) ENGINE=InnoDB AUTO_INCREMENT=1507299 DEFAULT CHARSET=utf8 1 row in set (0.00 sec) //删除no_index和title的索引 mysql> alter table article drop key key_index; Query OK, 0 rows affected (0.05 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> alter table article drop key key_no_index; Query OK, 0 rows affected (0.03 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> show create table article\G; *************************** 1. row *************************** Table: article Create Table: CREATE TABLE `article` ( `id` int(11) NOT NULL AUTO_INCREMENT, `no_index` int(11) DEFAULT NULL, `title` varchar(30) NOT NULL DEFAULT '', `add_time` datetime DEFAULT NULL, PRIMARY KEY (`id`), KEY `index_no_index_title` (`no_index`,`title`) ) ENGINE=InnoDB AUTO_INCREMENT=1507299 DEFAULT CHARSET=utf8 1 row in set (0.00 sec) //复合索引使用情况 mysql> explain select * from article where title='ddsd1123d' and no_index=77777\G; *************************** 1. row *************************** id: 1 select_type: SIMPLE table: article partitions: NULL type: ref possible_keys: index_no_index_title key: index_no_index_title key_len: 97 ref: const,const rows: 1 filtered: 100.00 Extra: NULL 1 row in set, 1 warning (0.00 sec) mysql> explain select * from article where no_index=77777\G; *************************** 1. row *************************** id: 1 select_type: SIMPLE table: article partitions: NULL type: ref possible_keys: index_no_index_title key: index_no_index_title key_len: 5 ref: const rows: 1 filtered: 100.00 Extra: NULL 1 row in set, 1 warning (0.00 sec)
我们可以定义(程序员)一个sql语句执行的最大执行时间,如果发现某条sql语句的执行时间超过我们所规定的时间界限,那么这条sql就会被记录下来.
先开启慢日志查询
查看慢日志配置
mysql> show variables like '%slow_query%'; +---------------------+--------------------------------------------------+ | Variable_name | Value | +---------------------+--------------------------------------------------+ | slow_query_log | OFF | | slow_query_log_file | /usr/local/mysql/data/caredeMacBook-Pro-slow.log | +---------------------+--------------------------------------------------+ 2 rows in set (0.00 sec)
开启慢日志查询
mysql> set global slow_query_log=on; Query OK, 0 rows affected (0.00 sec)
再次检查慢日志配置
mysql> show variables like '%slow_query%'; +---------------------+--------------------------------------------------+ | Variable_name | Value | +---------------------+--------------------------------------------------+ | slow_query_log | ON | | slow_query_log_file | /usr/local/mysql/data/caredeMacBook-Pro-slow.log | +---------------------+--------------------------------------------------+ 2 rows in set (0.00 sec)
去mysql配置文件my.ini中指定sql语句的界限时间和慢日志文件的路径
慢日志的名称，默认保存在mysql目录下面的data目录下面
log-slow-queries = 'man.txt'
设置一个界限时间
long-query-time=5
重启
通过profile工具分析一条sql语句的时间消耗在哪里
开启profile
执行一条SQL，(开启之后执行的所有SQL语句都会被记录下来
，以查看某条sql语句的具体执行时间耗费哪里)
根据query_id查找到具体的SQL
实例：
//查看profile设置 mysql> show variables like '%profil%'; +------------------------+-------+ | Variable_name | Value | +------------------------+-------+ | have_profiling | YES | | profiling | OFF |//未开启状态 | profiling_history_size | 15 | +------------------------+-------+ 3 rows in set (0.00 sec) //开启操作 mysql> set profiling = on; Query OK, 0 rows affected, 1 warning (0.00 sec) //查看是否开启成功 mysql> show variables like '%profil%'; +------------------------+-------+ | Variable_name | Value | +------------------------+-------+ | have_profiling | YES | | profiling | ON |//开启成功 | profiling_history_size | 15 | +------------------------+-------+ 3 rows in set (0.00 sec)
具体查询
mysql> select * from article where no_index=666666; +--------+----------+-----------+---------------------+ | id | no_index | title | add_time | +--------+----------+-----------+---------------------+ | 666666 | 666666 | ddsd1123d | 2019-05-15 23:13:55 | +--------+----------+-----------+---------------------+ 1 row in set (0.02 sec) mysql> show profiles; +----------+------------+---------------------------------------------+ | Query_ID | Duration | Query | +----------+------------+---------------------------------------------+ | 1 | 0.00150700 | show variables like '%profil%' | | 2 | 0.01481100 | select * from article where no_index=666666 | +----------+------------+---------------------------------------------+ 2 rows in set, 1 warning (0.00 sec) mysql> show profile for query 2; +----------------------+----------+ | Status | Duration | +----------------------+----------+ | starting | 0.000291 | | checking permissions | 0.000007 | | Opening tables | 0.012663 |//打开表 | init | 0.000050 | | System lock | 0.000009 | | optimizing | 0.000053 | | statistics | 0.001566 | | preparing | 0.000015 | | executing | 0.000002 | | Sending data | 0.000091 |//磁盘上的发送数据 | end | 0.000004 | | query end | 0.000007 | | closing tables | 0.000006 | | freeing items | 0.000037 | | cleaning up | 0.000010 | +----------------------+----------+ 15 rows in set, 1 warning (0.01 sec)
위 내용은 MySQL 인덱스 상세 설명+설명의 상세 내용입니다. 자세한 내용은 PHP 중국어 웹사이트의 기타 관련 기사를 참조하세요!
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