mysql优化篇（基于索引）

[root@lgh mysql]# ./bin/mysqldumpslow --help
Usage: mysqldumpslow [ OPTS... ] [ LOGS... ]

Parse and summarize the MySQL slow query log. Options are

  --verbose    verbose
  --debug      debug
  --help       write this text to standard output

  -v           verbose
  -d           debug
  -s ORDER     what to sort by (al, at, ar, c, l, r, t), ‘at‘ is default  #按照某种方式排序，默认at
                al: average lock time #平均锁定时间
                ar: average rows sent #平均返回记录数
                at: average query time #平均查询时间
                 c: count #访问次数
                 l: lock time #锁定时间
                 r: rows sent #返回记录
                 t: query time #查询时间
  -r           reverse the sort order (largest last instead of first) #倒序
  -t NUM       just show the top n queries  #topN
  -a           don‘t abstract all numbers to N and strings to ‘S‘
  -n NUM       abstract numbers with at least n digits within names
  -g PATTERN   grep: only consider stmts that include this string  #正则
  -h HOSTNAME  hostname of db server for *-slow.log filename (can be wildcard),
               default is ‘*‘, i.e. match all
  -i NAME      name of server instance (if using mysql.server startup script)
  -l           don‘t subtract lock time from total time #总时间（包括锁定时间）

语法：explain +  sql查询

SHOW PROFILE [type [, type] ... ]
    [FOR QUERY n]
    [LIMIT row_count [OFFSET offset]]

type: {
    ALL  #显示所有的开销信息
  | BLOCK IO #显示块IO开销
  | CONTEXT SWITCHES #上下文切换开销
  | CPU #显示CPU开销信息
  | IPC #显示发送和接收开销信息
  | MEMORY #显示内存开销信息
  | PAGE FAULTS #显示页面错误开销信息
  | SOURCE #显示和Source_function，Source_file，Source_line相关的开销信息
  | SWAPS #显示交换次数开销信息
}

mysql> explain select * from department d left join user u on u.d_id = d.id order by d.d_name; #在没有索引的情况下，除了全表扫描，还有临时表，filesort
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------------------------------------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra                                              |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------------------------------------------+
|  1 | SIMPLE      | d     | NULL       | ALL  | NULL          | NULL | NULL    | NULL |    6 |   100.00 | Using temporary; Using filesort                    |
|  1 | SIMPLE      | u     | NULL       | ALL  | NULL          | NULL | NULL    | NULL |    9 |   100.00 | Using where; Using join buffer (Block Nested Loop) |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------------------------------------------+
2 rows in set, 1 warning (0.00 sec)

mysql> explain select * from department d left join user u on u.d_id = d.id order by d.id;#在没有索引的情况下，除了全表扫描，还有临时表，filsort
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------------------------------------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra                                              |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------------------------------------------+
|  1 | SIMPLE      | d     | NULL       | ALL  | NULL          | NULL | NULL    | NULL |    6 |   100.00 | Using temporary; Using filesort                    |
|  1 | SIMPLE      | u     | NULL       | ALL  | NULL          | NULL | NULL    | NULL |    9 |   100.00 | Using where; Using join buffer (Block Nested Loop) |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------------------------------------------+
2 rows in set, 1 warning (0.00 sec)

mysql> create index idx_d_id on user(d_id);  #创建索引
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> explain select * from department d left join user u on u.d_id = d.id order by d.id; #创建索引后user表的rows为1，没有使用filesort和临时表
+----+-------------+-------+------------+-------+---------------+----------+---------+----------------------+------+----------+-------+
| id | select_type | table | partitions | type  | possible_keys | key      | key_len | ref                  | rows | filtered | Extra |
+----+-------------+-------+------------+-------+---------------+----------+---------+----------------------+------+----------+-------+
|  1 | SIMPLE      | d     | NULL       | index | NULL          | PRIMARY  | 4       | NULL                 |    6 |   100.00 | NULL  |
|  1 | SIMPLE      | u     | NULL       | ref   | idx_d_id      | idx_d_id | 5       | foundation_item.d.id |    1 |   100.00 | NULL  |
+----+-------------+-------+------------+-------+---------------+----------+---------+----------------------+------+----------+-------+
2 rows in set, 1 warning (0.00 sec)

mysql> explain select * from department d left join user u on u.d_id = d.id order by u.d_id; #把排序条件换成user的字段后，使用了临时表和filesort
+----+-------------+-------+------------+------+---------------+----------+---------+----------------------+------+----------+---------------------------------+
| id | select_type | table | partitions | type | possible_keys | key      | key_len | ref                  | rows | filtered | Extra                           |
+----+-------------+-------+------------+------+---------------+----------+---------+----------------------+------+----------+---------------------------------+
|  1 | SIMPLE      | d     | NULL       | ALL  | NULL          | NULL     | NULL    | NULL                 |    6 |   100.00 | Using temporary; Using filesort |
|  1 | SIMPLE      | u     | NULL       | ref  | idx_d_id      | idx_d_id | 5       | foundation_item.d.id |    1 |   100.00 | NULL                            |
+----+-------------+-------+------------+------+---------------+----------+---------+----------------------+------+----------+---------------------------------+
2 rows in set, 1 warning (0.00 sec)
mysql> explain select * from department d left join user u on u.d_id = d.id order by d.d_name; #把排序字段换成department表的d_name列（没有索引），使用了filesort
+----+-------------+-------+------------+------+---------------+----------+---------+----------------------+------+----------+----------------+
| id | select_type | table | partitions | type | possible_keys | key      | key_len | ref                  | rows | filtered | Extra          |
+----+-------------+-------+------------+------+---------------+----------+---------+----------------------+------+----------+----------------+
|  1 | SIMPLE      | d     | NULL       | ALL  | NULL          | NULL     | NULL    | NULL                 |    6 |   100.00 | Using filesort |
|  1 | SIMPLE      | u     | NULL       | ref  | idx_d_id      | idx_d_id | 5       | foundation_item.d.id |    1 |   100.00 | NULL           |
+----+-------------+-------+------------+------+---------------+----------+---------+----------------------+------+----------+----------------+
2 rows in set, 1 warning (0.00 sec)


mysql> explain select * from department d inner join user u on u.d_id = d.id order by d.d_name,u.id; #使用了user表的id排序，新增临时表
+----+-------------+-------+------------+------+---------------+----------+---------+----------------------+------+----------+---------------------------------+
| id | select_type | table | partitions | type | possible_keys | key      | key_len | ref                  | rows | filtered | Extra                           |
+----+-------------+-------+------------+------+---------------+----------+---------+----------------------+------+----------+---------------------------------+
|  1 | SIMPLE      | d     | NULL       | ALL  | PRIMARY       | NULL     | NULL    | NULL                 |    6 |   100.00 | Using temporary; Using filesort |
|  1 | SIMPLE      | u     | NULL       | ref  | idx_d_id      | idx_d_id | 5       | foundation_item.d.id |    1 |   100.00 | NULL                            |
+----+-------------+-------+------------+------+---------------+----------+---------+----------------------+------+----------+---------------------------------+
2 rows in set, 1 warning (0.00 sec)

mysql> explain select d.* from department d inner join user u on u.d_id = d.id order by d.d_name,u.id; #这里只返回department表的全部列，还是使用了临时表和filesort
+----+-------------+-------+------------+------+---------------+----------+---------+----------------------+------+----------+---------------------------------+
| id | select_type | table | partitions | type | possible_keys | key      | key_len | ref                  | rows | filtered | Extra                           |
+----+-------------+-------+------------+------+---------------+----------+---------+----------------------+------+----------+---------------------------------+
|  1 | SIMPLE      | d     | NULL       | ALL  | PRIMARY       | NULL     | NULL    | NULL                 |    6 |   100.00 | Using temporary; Using filesort |
|  1 | SIMPLE      | u     | NULL       | ref  | idx_d_id      | idx_d_id | 5       | foundation_item.d.id |    1 |   100.00 | Using index                     |
+----+-------------+-------+------------+------+---------------+----------+---------+----------------------+------+----------+---------------------------------+
2 rows in set, 1 warning (0.00 sec)

mysql> explain select d.* from department d inner join user u on u.d_id = d.id order by d.d_name; #去掉user的id列排序后少了临时表
+----+-------------+-------+------------+------+---------------+----------+---------+----------------------+------+----------+----------------+
| id | select_type | table | partitions | type | possible_keys | key      | key_len | ref                  | rows | filtered | Extra          |
+----+-------------+-------+------------+------+---------------+----------+---------+----------------------+------+----------+----------------+
|  1 | SIMPLE      | d     | NULL       | ALL  | PRIMARY       | NULL     | NULL    | NULL                 |    6 |   100.00 | Using filesort |
|  1 | SIMPLE      | u     | NULL       | ref  | idx_d_id      | idx_d_id | 5       | foundation_item.d.id |    1 |   100.00 | Using index    |
+----+-------------+-------+------------+------+---------------+----------+---------+----------------------+------+----------+----------------+
2 rows in set, 1 warning (0.00 sec)

mysql> explain select d.* from department d inner join user u on u.d_id = d.id order by d.id; #使用department的id排序，没了filesort
+----+-------------+-------+------------+-------+---------------+----------+---------+----------------------+------+----------+-------------+
| id | select_type | table | partitions | type  | possible_keys | key      | key_len | ref                  | rows | filtered | Extra       |
+----+-------------+-------+------------+-------+---------------+----------+---------+----------------------+------+----------+-------------+
|  1 | SIMPLE      | d     | NULL       | index | PRIMARY       | PRIMARY  | 4       | NULL                 |    6 |   100.00 | NULL        |
|  1 | SIMPLE      | u     | NULL       | ref   | idx_d_id      | idx_d_id | 5       | foundation_item.d.id |    1 |   100.00 | Using index |
+----+-------------+-------+------------+-------+---------------+----------+---------+----------------------+------+----------+-------------+
2 rows in set, 1 warning (0.00 sec)

mysql> create index d_word on user(word); #创建索引
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> explain select * from user where word= ‘c写代码2‘; #使用等值查询，使用到了索引
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key    | key_len | ref   | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------+
|  1 | SIMPLE      | user  | NULL       | ref  | d_word        | d_word | 203     | const |    1 |   100.00 | NULL  |
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)

mysql> explain select * from user where left(word,1)= ‘c‘; #在where中使用了函数或者计算，全表扫描没有使用到索引
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
|  1 | SIMPLE      | user  | NULL       | ALL  | NULL          | NULL | NULL    | NULL |    9 |   100.00 | Using where |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)

order by使用索引最左前缀
- order by a
- order by a,b
- order by a,b,c
- order by a desc, b desc, c desc 

如果where使用索引的最左前缀定义为常量，则order by能使用索引
- where a=const order by b,c
- where a=const and b=const order by c
- where a=const and b > const order by b,c

不能使用索引进行排序
- order by a , b desc ,c desc  --排序不一致
- where d=const order by b,c   --a丢失
- where a=const order by c     --b丢失
- where a=const order by b,d   --d不是索引的一部分
- where a in(...) order by b,c --a属于范围查询

create table test(
id int(11) primary key auto_increment,
name varchar(56),
salary double
);

delimiter $$
create function rand_string(n int) returns varchar(255)
begin
    declare char_str varchar(100) default ‘abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ‘;
    declare result_str varchar(255) default ‘‘;
    declare i int default 0;
    while i<n do
    set result_str = concat(result_str,SUBSTRING(char_str,FLOOR(1+rand()*52),1 ));
    set i=i+1;
    end while;
    return result_str;
end $$

delimiter $$
create procedure insert_tab(in start int(10),in max_num int(10))
begin
    declare i  int default 0;
    set autocommit = 0;
    repeat
    set i=i+1;
    insert into test(name,salary) values(rand_string(6),rand()*5000);
    until i = max_num
    end repeat;
    commit;
end $$

delimiter ;

call insert_tab(1,1000000);