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First, the transaction
1. The transaction leads
Services are widely used in a variety of scenarios ordering system, banking system.
For example:
A user and user B is the bank's depositors, and now to give A B transfer $ 500, you need to do the following things:
account balance check of A> 500 yuan;
A accounts deducted 500 yuan;
B accounts increased by 500 yuan.
The normal process to go down, buckle up account A 500, B 500 plus account;
that if the A accounts after deduction of the money, the system is out of order, will be losing 500 A and B did not receive this belong to him 500.
Above cases, it hides a prerequisite: A and B plus money deducting money, at the same time either succeed or fail at the same time. Demand affairs in this.
2. transaction definition
A transaction is a sequence of operations, these operations are either executed or not executed, it is an indivisible unit of work.
For example, bank transfer work: another account and grants from a debit account, these two operations are either executed or not executed. Therefore, we should see them as a business.
A transaction is a database maintaining data consistency of the unit, at the end of each transaction, can maintain data consistency.
Then at least three steps:
(1) check the account balance is greater than or equal to $ 1 100;
(2) subtracting 1 from the account balance to $ 100; and
(3) an increase of $ 100 2 balance in your account.
begin;
update bank1 set money = money - 100 where id = 1;
At this point there is no commit, the data will not change when the query that reflects the isolation of things.
update bank2 set money = money + 100 where id = 1;
commit;
At this time, the data in the two tables are changed, reducing a 100, a 100 increase.
More than two steps to form a complete transaction.
Every time does not automatically submitted after executing a SQL statement after opening the transaction, to be submitted in order to operate successfully.
3. Characteristics of the four transactions (ACID)
(1) atomicity (Atomicity):
A transaction is considered an integral part of the smallest unit of work, all the operations of the entire transaction either all submitted successfully, or all fail rollback for a transaction, it is not possible to perform only where the part of the operation, which is the atomicity of transactions.
(2) Consistency (Consistency):
database is always a state transition from a state to another consistent consistency.
In the previous example, the consistency is ensured, even when the system is executed between the two update statements collapse, bank accounts will not lose $ 100, because the transaction did not submit the final, so the modifications made to the transaction will not saved to the database.
(3) isolation (Isolation):
Generally speaking, the firm made a modification before final submission, other transactions are not visible.
In the previous example, when the first update after executing the statement, the fourth sentence has not yet started, this time there is another account of a summary of the program is running, it saw the balance of the account has not been a minus $ 100 .
In a command line, open a transaction
begin;
update goods set name = 'palyer' where id = 3;
Uncommitted
perform another operation on another command line
update goods set name = 'Player' where id = 3;
Appears blocked because a previous command line does not commit the transaction, at a time of operation, the operation of other databases will be locked, ie before, thus ensuring data consistency.
(4) persistent (Durability):
Once the transaction commits, modify it made permanently saved to the database.
At this point even if the system crashes, the modified data will not be lost.
4. transactional operations
Table of engine type must be innodb types can use the transaction, which is the default engine mysql table.
Open transactions :
Grammar: start transation;or begin;
open a transaction executed after modification commands, change will maintain the local cache, rather than maintain the physical table.
Commit the transaction :
syntax: commit;
the data cache changes to the physical maintenance of the table.
Roll back the transaction :
Syntax: rollback;
give up the data cache changes.
Exercise :
Now an operation in a transaction to 2 100 rpm, while the other 1 to 3 in the transaction 100. The transfer
data is as follows
+----+-----+
| id | num |
+----+-----+
| 1 | 100 |
| 2 | 200 |
| 3 | 0 |
+----+-----+
The process operation is shown
after the transaction submitted 1, two pairs id1 change the transaction would be an error, and therefore need to roll back, thus ensuring data consistency.
Modify data command automatically triggers affairs, including insert, update, delete;
data if the operation involves many changes to the database data, and success with success, otherwise they will be rolled together before, the need to manually in SQL statements open affairs.
Second, the index
1. introduction
在图书馆中是如何找到一本书的？
一般的应用系统对比数据库的读写比例在10:1左右(即有10次查询操作时有1次写的操作)，而且插入操作和更新操作很少出现性能问题，遇到最多、最容易出问题还是一些复杂的查询操作，所以查询语句的优化显然是重中之重。
当数据库中数据量很大时，查找数据会变得很慢，所以引入索引进行优化。
2.定义
索引是一种特殊的文件(InnoDB数据表上的索引是表空间的一个组成部分)，它们包含着对数据表里所有记录的引用指针。
通俗地说，数据库索引就像一本书前面的目录，它们包含着对数据表里所有记录的引用指针。
索引的目的：
索引的目的在于提高查询效率，可以类比字典，如果要查“mysql”这个单词，我们肯定需要定位到m字母，然后从下往下找到y字母，再找到剩下的sql。
索引原理：
生活中随处可见索引的例子，如词典、火车站的车次表、图书的目录等。它们的原理都是一样的，通过不断的缩小想要获得数据的范围来筛选出最终想要的结果，同时把随机的事件变成顺序的事件，也就是我们总是通过同一种查找方式来锁定数据。
数据库也是一样，但显然要复杂许多，因为不仅面临着等值查询，还有范围查询(>、<、between、in)、模糊查询(like)、并集查询(or)等等。
如下图
索引使用的数据结构一般是B树。
索引分为：
- 单值索引：单个字段；
- 复合索引：多个字段；
- 唯一索引：列的值必须唯一，应用于身份证号、电话号等。
3.索引的使用
查看索引：
语法：show index from 表名;
show index from money;
打印
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| money | 0 | PRIMARY | 1 | id | A | 3 | NULL | NULL | | BTREE | | |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.01 sec)
主键会自动创建索引；
创建索引：
语法：create index 字段名称 on 表名(字段名称(长度));
create index idx_num on money(num);
再查看索引
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| money | 0 | PRIMARY | 1 | id | A | 3 | NULL | NULL | | BTREE | | |
| money | 1 | idx_num | 1 | num | A | 2 | NULL | NULL | | BTREE | | |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
2 rows in set (0.00 sec)
如果指定字段是字符串，需要指定长度，建议长度与定义字段时的长度一致；
字段类型如果不是字符串，可以不填写长度部分。
创建唯一索引：
create unique index idx_num on money(num);
删除索引：
语法：drop index 索引名称 on 表名;
4.索引练习
创建测试表test：
create table test(title varchar(10));
使用python程序向表中加入十万条数据:
from pymysql import *
def main():
conn = connect(
host='127.0.0.1',
port=3306,
db='demo',
user='root',
passwd='root',
charset='utf8')
cur = conn.cursor()
for i in range(100000):
cur.execute('insert into test values("ts-%d")' % i)
conn.commit()
if __name__ == '__main__':
main()
开启运行时间监测：
set profiling=1;
查找第100000条数据：
select * from test where title='ts-99999';
打印
+----------+
| title |
+----------+
| ts-99999 |
+----------+
1 row in set (0.04 sec)
查看执行的时间：
show profiles;
打印
+----------+------------+-------------------------------------------+
| Query_ID | Duration | Query |
+----------+------------+-------------------------------------------+
| 1 | 0.03794450 | select * from test where title='ts-99999' |
+----------+------------+-------------------------------------------+
1 row in set, 1 warning (0.00 sec)
为表title_index的title列创建索引：
create index title_index on test(title(10));
再次执行查询语句：
select * from test where title='ts-99999';
打印
+----------+
| title |
+----------+
| ts-99999 |
+----------+
1 row in set (0.00 sec)
再次查看执行的时间:
show profiles;
打印
+----------+------------+---------------------------------------------+
| Query_ID | Duration | Query |
+----------+------------+---------------------------------------------+
| 1 | 0.03794450 | select * from test where title='ts-99999' |
| 2 | 0.26895350 | create index title_index on test(title(10)) |
| 3 | 0.00031875 | select * from test where title='ts-99999' |
+----------+------------+---------------------------------------------+
3 rows in set, 1 warning (0.00 sec)
显然，建立了索引后查询速度有了很大提升，即建立索引可以大幅提高查询效率。
适合建立索引的情况：
- 主键自动建立索引；
- 频繁作为查询条件的字段应该建立索引；
- 查询中与其他表关联的字段,外键关系建立索引；
- 在高并发的情况下创建复合索引；
- 查询中排序的字段,排序字段若通过索引去访问将大大提高排序速度 (建立索引的顺序跟排序的顺序保持一致)。
不适合建立索引的情况：
- 频繁更新的字段不适合建立索引；
- where条件里面用不到的字段不创建索引；
- 表记录太少,当表中数据量超过三百万条数据,可以考虑建立索引；
- 数据重复且平均的表字段,比如性别,国籍。
三、账户管理
在生产环境下操作数据库时，绝对不可以使用root账户连接，而是创建特定的账户，授予这个账户特定的操作权限，然后连接进行操作，主要的操作就是数据的crud。
MySQL账户体系：
根据账户所具有的权限的不同，MySQL的账户可以分为以下几种：
- 服务实例级账号：启动了一个mysqld，即为一个数据库实例；如果某用户如root,拥有服务实例级分配的权限，那么该账号就可以删除所有的数据库、连同这些库中的表；
- 数据库级别账号：对特定数据库执行增删改查的所有操作；
- 数据表级别账号：对特定表执行增删改查等所有操作；
- 字段级别的权限：对某些表的特定字段进行操作；
- 存储程序级别的账号：对存储程序进行增删改查的操作。
账户的操作主要包括创建账户、删除账户、修改密码、授权权限等。
授予权限：
需要使用实例级账户登录后操作，以root为例
主要操作包括：
（1）查看所有用户：
所有用户及权限信息存储在mysql数据库的user表中；
查看user表的结构：
use mysql;
desc user;
打印
+------------------------+-----------------------------------+------+-----+-----------------------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------------------+-----------------------------------+------+-----+-----------------------+-------+
| Host | char(60) | NO | PRI | | |
| User | char(32) | NO | PRI | | |
| Select_priv | enum('N','Y') | NO | | N | |
| Insert_priv | enum('N','Y') | NO | | N | |
| Update_priv | enum('N','Y') | NO | | N | |
| Delete_priv | enum('N','Y') | NO | | N | |
| Create_priv | enum('N','Y') | NO | | N | |
| Drop_priv | enum('N','Y') | NO | | N | |
| Reload_priv | enum('N','Y') | NO | | N | |
| Shutdown_priv | enum('N','Y') | NO | | N | |
| Process_priv | enum('N','Y') | NO | | N | |
| File_priv | enum('N','Y') | NO | | N | |
| Grant_priv | enum('N','Y') | NO | | N | |
| References_priv | enum('N','Y') | NO | | N | |
| Index_priv | enum('N','Y') | NO | | N | |
| Alter_priv | enum('N','Y') | NO | | N | |
| Show_db_priv | enum('N','Y') | NO | | N | |
| Super_priv | enum('N','Y') | NO | | N | |
| Create_tmp_table_priv | enum('N','Y') | NO | | N | |
| Lock_tables_priv | enum('N','Y') | NO | | N | |
| Execute_priv | enum('N','Y') | NO | | N | |
| Repl_slave_priv | enum('N','Y') | NO | | N | |
| Repl_client_priv | enum('N','Y') | NO | | N | |
| Create_view_priv | enum('N','Y') | NO | | N | |
| Show_view_priv | enum('N','Y') | NO | | N | |
| Create_routine_priv | enum('N','Y') | NO | | N | |
| Alter_routine_priv | enum('N','Y') | NO | | N | |
| Create_user_priv | enum('N','Y') | NO | | N | |
| Event_priv | enum('N','Y') | NO | | N | |
| Trigger_priv | enum('N','Y') | NO | | N | |
| Create_tablespace_priv | enum('N','Y') | NO | | N | |
| ssl_type | enum('','ANY','X509','SPECIFIED') | NO | | | |
| ssl_cipher | blob | NO | | NULL | |
| x509_issuer | blob | NO | | NULL | |
| x509_subject | blob | NO | | NULL | |
| max_questions | int(11) unsigned | NO | | 0 | |
| max_updates | int(11) unsigned | NO | | 0 | |
| max_connections | int(11) unsigned | NO | | 0 | |
| max_user_connections | int(11) unsigned | NO | | 0 | |
| plugin | char(64) | NO | | mysql_native_password | |
| authentication_string | text | YES | | NULL | |
| password_expired | enum('N','Y') | NO | | N | |
| password_last_changed | timestamp | YES | | NULL | |
| password_lifetime | smallint(5) unsigned | YES | | NULL | |
| account_locked | enum('N','Y') | NO | | N | |
+------------------------+-----------------------------------+------+-----+-----------------------+-------+
45 rows in set (0.00 sec)
主要字段说明：
Host表示允许访问的主机；
User表示用户名；
authentication_string表示密码，为加密后的值。
查看所有用户：
select host,user,authentication_string from user;
+-----------+---------------+-------------------------------------------+
| host | user | authentication_string |
+-----------+---------------+-------------------------------------------+
| localhost | root | *81F5E21E35407D884A6CD4A731AEBFB6AF209E1B |
| localhost | mysql.session | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
| localhost | mysql.sys | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
| 127.0.0.1 | Tom | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |
| localhost | Tom2 | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |
+-----------+---------------+-------------------------------------------+
5 rows in set (0.00 sec)
（2）创建账户、授权
需要使用实例级账户登录后操作，以root为例
常用权限主要包括：create、alter、drop、insert、update、delete、select
如果分配所有权限，可以使用all privileges
语法：
grant 权限列表 on 数据库 to '用户名'@'访问主机' identified by '密码';
grant select on jingdong.* to 'Leo'@'localhost' identified by '123456';
--创建一个Mary的账号，密码为12345678，可以任意电脑进行链接访问, 并且对jd数据库中的所有表拥有所有权限
grant all privileges on jd.* to "Mary"@"%" identified by "12345678"
--刷新权限
flush privileges;
说明：
可以操作数据库的所有表，方式为:jingdong.*；
访问主机通常使用 百分号% 表示此账户可以使用任何ip的主机登录访问此数据库；
访问主机可以设置成 localhost或具体的ip，表示只允许本机或特定主机访问。
查看用户有哪些权限：
show grants for Leo@localhost;
打印
+---------------------------------------------------+
| Grants for Leo@localhost |
+---------------------------------------------------+
| GRANT USAGE ON *.* TO 'Leo'@'localhost' |
| GRANT SELECT ON `jingdong`.* TO 'Leo'@'localhost' |
+---------------------------------------------------+
2 rows in set (0.00 sec)
使用新创建的用户登录：
mysql -uLeo -p
查看数据库：
show databases;
打印
+--------------------+
| Database |
+--------------------+
| information_schema |
| jingdong |
+--------------------+
2 rows in set (0.00 sec)
进行删除操作
use jingdong;
drop table goods;
打印
ERROR 1142 (42000): DROP command denied to user 'Leo'@'localhost' for table 'goods'
Error, command rejected because only gave Leo the permission to view, so you can not add, modify, delete operations.
Fourth, Introduction to database storage engine
1.MySQL architecture:
- The connection layer
- Service layer (core)
- Storage Engine layer
- File system
Figure:
service layer :
services layer is the core of MySQL, MySQL's core service layer in this layer, query parsing, SQL execution plan analysis, SQL execution plan optimization, query cache, as well as cross-Storage Engine functionality in this layer implements: stored procedures, triggers, and other views.
The figure is the internal structure of the service layer:
storage engine layer :
responsible for MySQL's data storage and extraction.
Query execution engine server communicates with the storage engine through the API, an interface screen through the differences between different storage engines.
MySQL uses plug-in storage engine. MySQL storage engine provides a number of us, each storage engines have different characteristics. We can according to different business characteristics, choose the most suitable storage engine.
If you are not satisfied with the performance of the storage engine, you can get the performance you want to achieve by modifying the source code. For example Alibaba X-Engine, facebook and google to meet the needs of enterprises of all InnoDB storage engine have been expanded.
2. Storage Engine Operations
View storage engine:
show engines;
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine | Support | Comment | Transactions | XA | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| InnoDB | DEFAULT | Supports transactions, row-level locking, and foreign keys | YES | YES | YES |
| MRG_MYISAM | YES | Collection of identical MyISAM tables | NO | NO | NO |
| MEMORY | YES | Hash based, stored in memory, useful for temporary tables | NO | NO | NO |
| BLACKHOLE | YES | /dev/null storage engine (anything you write to it disappears) | NO | NO | NO |
| MyISAM | YES | MyISAM storage engine | NO | NO | NO |
| CSV | YES | CSV storage engine | NO | NO | NO |
| ARCHIVE | YES | Archive storage engine | NO | NO | NO |
| PERFORMANCE_SCHEMA | YES | Performance Schema | NO | NO | NO |
| FEDERATED | NO | Federated MySQL storage engine | NULL | NULL | NULL |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
9 rows in set (0.01 sec)
View the default storage engine:
show variables like '%storage_engines%';
+--------------------------+-------+
| Variable_name | Value |
+--------------------------+-------+
| disabled_storage_engines | |
+--------------------------+-------+
1 row in set, 1 warning (0.00 sec)
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