Mysql help命令（帮助信息）中文注解

获取mysql有关的帮助信息，直接在mysql提示符下输入help即可获得有关在mysql客户端相关的帮助信息。
这个方式与Oracle SQL*plus下的help 是类似的。
mysql> help

For information about MySQL products and services, visit:
  http://www.mysql.com/
For developer information, including the MySQL Reference Manual, visit:
  http://dev.mysql.com/
To buy MySQL Enterprise support, training, or other products, visit:
  https://shop.mysql.com/

List of all MySQL commands:
Note that all text commands must be first on line and end with ';'      
?     (\?) Synonym for `help'. 
clear   (\c) Clear the current input statement.               --清除当前输入的语句
connect  (\r) Reconnect to the server. Optional arguments are db and host.  --重新连接，通常用于被剔除或异常断开后重新连接，SQL*plus下也有这样一个connect命令
delimiter (\d) Set statement delimiter.                    --设置命令终止符，缺省为；，比如我们可以设定为/来表示语句结束 
edit   (\e) Edit command with $EDITOR.                   --编辑缓冲区的上一条SQL语句到文件，缺省调用vi，文件会放在/tmp路径下
ego    (\G) Send command to mysql server, display result vertically.    --控制结果显示为垂直显示
exit   (\q) Exit mysql. Same as quit.                   --退出mysql
go    (\g) Send command to mysql server.                 --发送命令到mysql服务
help   (\h) Display this help.
nopager  (\n) Disable pager, print to stdout.                --关闭页设置，打印到标准输出  
notee   (\t) Don't write into outfile.                   --关闭输出到文件
pager   (\P) Set PAGER [to_pager]. Print the query results via PAGER.    --设置pager方式，可以设置为调用more,less等等，主要是用于分页显示
print   (\p) Print current command.           
prompt  (\R) Change your mysql prompt.                   --改变mysql的提示符 
quit   (\q) Quit mysql.                             
rehash  (\#) Rebuild completion hash.                    --自动补齐相关对象名字  
source  (\.) Execute an SQL script file. Takes a file name as an argument. --执行脚本文件
status  (\s) Get status information from the server.            --获得状态信息
system  (\!) Execute a system shell command.                --执行系统命令   
tee    (\T) Set outfile [to_outfile]. Append everything into given outfile.--操作结果输出到文件 
use    (\u) Use another database. Takes database name as argument.     --切换数据库
charset  (\C) Switch to another charset. Might be needed for processing binlog with multi-byte charsets. --设置字符集
warnings (\W) Show warnings after every statement.              --打印警告信息
nowarning (\w) Don't show warnings after every statement.
--上面的所有命令，扩号内的为快捷操作，即只需要输入“\”+ 字母即可执行

For server side help, type 'help contents'  --注意这里的描述help contents将获得服务器端的相关帮助信息

--演示部分，演示常用命令
--connect命令
mysql> connect chardb localhost;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Connection id:  5
Current database: chardb

--设置分页，在多余一个页面显示时会不停的翻滚，用该命令可以设置分页，设置为调用系统命令
mysql> pager more      --设置为more方式
PAGER set to 'more'
mysql> select table_name,table_type,engine from information_schema.tables;  --该查询会超出一屏显示后按空格键会自动翻滚到下一屏
mysql> pager tail -5;    --设置输出尾部5行
PAGER set to 'tail -5'
mysql> select table_name,table_type,engine from information_schema.tables;
| setup_timers                 | BASE TABLE | PERFORMANCE_SCHEMA |
| threads                   | BASE TABLE | PERFORMANCE_SCHEMA |
| animals                   | BASE TABLE | InnoDB       |
| shop                     | BASE TABLE | InnoDB       |
+----------------------------------------------+-------------+--------------------+
92 rows in set (0.02 sec)

mysql> pager;        --查看当前的pager设置
PAGER set to 'tail -5'
mysql> nopager;       --切换到标准(缺省)pager方式
PAGER set to stdout

--tee命令，输出日志文件
mysql> tee /tmp/query.log          --开启输出到文件，相当与SQL*plus下的spool
Logging to file '/tmp/query.log'
mysql> select table_name,table_type,engine from information_schema.tables;
+----------------------------------------------+-------------+--------------------+
| table_name                  | table_type | engine       |
+----------------------------------------------+-------------+--------------------+
| CHARACTER_SETS                | SYSTEM VIEW | MEMORY       |
| COLLATIONS                  | SYSTEM VIEW | MEMORY       |
    .............
mysql> notee;                --关闭输出到文件，相当于SQL*Plus下的spool off
Outfile disabled.
mysql> system tail /tmp/query.log      --查看输出的日志文件
| setup_consumers               | BASE TABLE | PERFORMANCE_SCHEMA |
| setup_instruments              | BASE TABLE | PERFORMANCE_SCHEMA |
| setup_timers                 | BASE TABLE | PERFORMANCE_SCHEMA |
| threads                   | BASE TABLE | PERFORMANCE_SCHEMA |
| animals                   | BASE TABLE | InnoDB       |
| shop                     | BASE TABLE | InnoDB       |
+----------------------------------------------+-------------+--------------------+
92 rows in set (0.02 sec)    

--改变mysql提示符
mysql> prompt SessionA> 
PROMPT set to 'SessionA> '

--恢复到缺省提示符
SessionA> prompt;
Returning to default PROMPT of mysql> 

--执行sql脚本文件
mysql> system more query.sql  --注意，此时为当前目录
use chardb
select * from tb_isam;
mysql> source query.sql
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
+------+-------+
| id  | value |
+------+-------+
|  1 | a   |
|  2 | b   |
|  3 | c   |
|  4 | f   |
+------+-------+
4 rows in set (0.00 sec)

--获取状态信息
mysql> status;
--------------
mysql Ver 14.14 Distrib 5.5.37, for Linux (x86_64) using readline 5.1

Connection id:     6
Current database:    chardb
Current user:      root@localhost
SSL:          Not in use
Current pager:     less
Using outfile:     ''
Using delimiter:    ;
Server version:     5.5.37-log MySQL Community Server (GPL)
Protocol version:    10
Connection:       Localhost via UNIX socket
Server characterset:  latin1
Db   characterset:  utf8
Client characterset:  latin1
Conn. characterset:  latin1
UNIX socket:      /var/lib/mysql/mysql.sock
Uptime:         3 hours 10 min 59 sec

Threads: 1 Questions: 97 Slow queries: 0 Opens: 313 Flush tables: 1 Open tables: 51 Queries per second avg: 0.008
--------------

--修改客户端字符集
mysql> charset gbk;
Charset changed
mysql> \s
--------------
mysql Ver 14.14 Distrib 5.5.37, for Linux (x86_64) using readline 5.1

Connection id:     6
Current database:    chardb
Current user:      root@localhost
SSL:          Not in use
Current pager:     less
Using outfile:     ''
Using delimiter:    ;
Server version:     5.5.37-log MySQL Community Server (GPL)
Protocol version:    10
Connection:       Localhost via UNIX socket
Server characterset:  latin1
Db   characterset:  utf8
Client characterset:  gbk   ---客户端和conn端字符集都变成gbk了。
Conn. characterset:  gbk
UNIX socket:      /var/lib/mysql/mysql.sock
Uptime:         3 hours 13 min 33 sec

Threads: 1 Questions: 105 Slow queries: 0 Opens: 313 Flush tables: 1 Open tables: 51 Queries per second avg: 0.009
--------------

mysql> warnings;
Show warnings enabled.
mysql> selecs 1;
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 'selecs 1' at line 1
mysql> show warnings;
+-------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Level | Code | Message                                                                          |
+-------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Error | 1064 | 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 'selecs 1' at line 1 |
+-------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> show errors;
+-------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Level | Code | Message                                                                          |
+-------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Error | 1064 | 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 'selecs 1' at line 1 |
+-------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> nowarning;
Show warnings disabled.