在开发或测试环境在碰到mysql相关故障时，如果在没有网络的情况下，我们可能通过mysql自带的帮助信息获得相关的语法等相关信息。如果有网络的话当然可以查询官网或者百度，官网的文档链接http://dev.mysql.com/doc/。
1.mysql客户端的help
和oracle的sqlplus一样，可以通过mysql客户端的一些设置更改客户端的一些设置，包括输入/输出方式，提示符，客户端字符集，警告信息是否显示等等。
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 $EDITOR. --编辑缓冲区的上一条SQL语句到文件，缺省调用vi，文件会放在/tmp路径下
ego (\G) Send command to mysql server, display result vertically. --控制结果显示为垂直显示
exit (\q) Exit mysql. Same as quit. --退出mysql
go (\g) Send command to mysql server. --发送命令到mysql服务
help (\h) Display this help.
nopager (\n) Disable pager, print to stdout. --关闭页设置，打印到标准输出
notee (\t) Don't write into outfile. --关闭输出到文件
pager (\P) Set PAGER [to_pager]. Print the query results via PAGER. --设置pager方式，可以设置为调用more,less等等，主要是用于分页显示
print (\p) Print current command.
prompt (\R) Change your mysql prompt. --改变mysql的提示符
quit (\q) Quit mysql.
rehash (\#) Rebuild completion hash. --自动补齐相关对象名字
source (\.) Execute an SQL script file. Takes a file name as an argument. --执行脚本文件
status (\s) Get status information from the server. --获得状态信息
system (\!) Execute a system shell command. --执行系统命令
tee (\T) Set outfile [to_outfile]. Append everything into given outfile.--操作结果输出到文件
use (\u) Use another database. Takes database name as argument. --切换数据库
charset (\C) Switch to another charset. Might be needed for processing binlog with multi-byte charsets. --设置字符集
warnings (\W) Show warnings after every statement. --打印警告信息
nowarning (\w) Don't show warnings after every statement.
--上面的所有命令，扩号内的为快捷操作，即只需要输入“\”+ 字母即可执行
For server side help, type 'help contents' --注意这里的描述help contents将获得服务器端的相关帮助信息测试其中的几个：
\c就是表示当前的命令取消
mysql> select aaaa \c\r或connect 就是重新连接数据库
mysql> \r l5m
Connection id: 9
Current database: l5mpager的输出方式
mysql> pager more
PAGER set to 'more'
mysql> select table_name,table_type,engine from information_schema.tables;
| ROUTINES | SYSTEM VIEW | InnoDB
|
| SCHEMATA | SYSTEM VIEW | MEMORY
|
---More---
#以more的方式显示，需要按任一键后显示下一页
mysql> pager tail -5;
PAGER set to 'tail -5'
mysql> select table_name,table_type,engine from information_schema.tables;
| x$wait_classes_global_by_latency | VIEW | NULL |
| x$waits_by_host_by_latency | VIEW | NULL |
| x$waits_by_user_by_latency | VIEW | NULL |
| x$waits_global_by_latency | VIEW | NULL |
+------------------------------------------------------+-------------+--------------------+
287 rows in set (0.00 sec)
#只显示最后5行的数据
mysql> nopager;
PAGER set to stdout
#改为默认方法system 是执行shell命令，而source是直接执行脚本里面的命令
mysql> system more query.sql
use l5m
#相当于在shell环境下执行more query.sql命令
mysql> source query.sql
Database changed
#直接执行query.sql的脚本prompt修改提示符
mysql> prompt SessionA>
PROMPT set to 'SessionA>'
SessionA>prompt;
Returning to default PROMPT of mysql>charset设置客户端的字符集
mysql> charset gbk;
Charset changed
mysql> \s
--------------
mysql Ver 14.14 Distrib 5.7.21, for linux-glibc2.12 (x86_64) using EditLine wrapper
Connection id: 12
Current database: l5m
Current user: root@localhost
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server version: 5.7.21-log MySQL Community Server (GPL)
Protocol version: 10
Connection: Localhost via UNIX socket
Server characterset: utf8
Db characterset: utf8
Client characterset: gbk
Conn. characterset: gbk
UNIX socket: /u01/mysql/mysql.sock
Uptime: 1 hour 4 min 12 sec
Threads: 1 Questions: 71 Slow queries: 0 Opens: 124 Flush tables: 1 Open tables: 117 Queries per second avg: 0.018
--------------
mysql> charset utf8
Charset changed
mysql> \s
--------------
mysql Ver 14.14 Distrib 5.7.21, for linux-glibc2.12 (x86_64) using EditLine wrapper
Connection id: 12
Current database: l5m
Current user: root@localhost
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server version: 5.7.21-log MySQL Community Server (GPL)
Protocol version: 10
Connection: Localhost via UNIX socket
Server characterset: utf8
Db characterset: utf8
Client characterset: utf8
Conn. characterset: utf8
UNIX socket: /u01/mysql/mysql.sock
Uptime: 1 hour 4 min 28 sec
Threads: 1 Questions: 75 Slow queries: 0 Opens: 124 Flush tables: 1 Open tables: 117 Queries per second avg: 0.019
--------------2.服务器端相关的help
客户端help的最后一行显示For server side help, type 'help contents'
mysql> help contents;
You asked for help about help category: "Contents"
For more information, type 'help <item>', where <item> is one of the following
categories:
Account Management
Administration
Compound Statements
Data Definition
Data Manipulation
Data Types
Functions
Functions and Modifiers for Use with GROUP BY
Geographic Features
Help Metadata
Language Structure
Plugins
Procedures
Storage Engines
Table Maintenance
Transactions
User-Defined Functions
Utility要查询那一个部分的内容，直接输入help + 内容，如下
mysql> help Account Management
You asked for help about help category: "Account Management"
For more information, type 'help <item>', where <item> is one of the following
topics:
ALTER USER
CREATE USER
DROP USER
GRANT
RENAME USER
REVOKE
SET PASSWORD
mysql> help Administration
You asked for help about help category: "Administration"
For more information, type 'help <item>', where <item> is one of the following
topics:
BINLOG
CACHE INDEX
FLUSH
FLUSH QUERY CACHE
HELP COMMAND
KILL
LOAD INDEX
RESET
SET
SET CHARACTER SET
SET NAMES
SHOW
SHOW BINARY LOGS
SHOW BINLOG EVENTS
SHOW CHARACTER SET
SHOW COLLATION
SHOW COLUMNS
SHOW CREATE DATABASE
SHOW CREATE EVENT
SHOW CREATE FUNCTION
SHOW CREATE PROCEDURE
SHOW CREATE TABLE
SHOW CREATE TRIGGER
SHOW CREATE USER
SHOW CREATE VIEW
SHOW DATABASES
SHOW ENGINE
SHOW ENGINES
SHOW ERRORS
SHOW EVENTS
SHOW FUNCTION CODE
SHOW FUNCTION STATUS
SHOW GRANTS
SHOW INDEX
SHOW MASTER STATUS
SHOW OPEN TABLES
SHOW PLUGINS
SHOW PRIVILEGES
SHOW PROCEDURE CODE
SHOW PROCEDURE STATUS
SHOW PROCESSLIST
SHOW PROFILE
SHOW PROFILES
SHOW RELAYLOG EVENTS
SHOW SLAVE HOSTS
SHOW SLAVE STATUS
SHOW STATUS
SHOW TABLE STATUS
SHOW TABLES
SHOW TRIGGERS
SHOW VARIABLES
SHOW WARNINGS
SHUTDOWN可以接着help下面的flush:
mysql> help flush;
Name: 'FLUSH'
Description:
Syntax:
FLUSH [NO_WRITE_TO_BINLOG | LOCAL] {
flush_option [, flush_option] ...
| tables_option
}
flush_option: {
BINARY LOGS
| DES_KEY_FILE
| ENGINE LOGS
| ERROR LOGS
| GENERAL LOGS
| HOSTS
| LOGS
| PRIVILEGES
| OPTIMIZER_COSTS
| QUERY CACHE
| RELAY LOGS [FOR CHANNEL channel]
| SLOW LOGS
| STATUS
| USER_RESOURCES
}
tables_option: {
TABLES
| TABLES tbl_name [, tbl_name] ...
| TABLES WITH READ LOCK
| TABLES tbl_name [, tbl_name] ... WITH READ LOCK
| TABLES tbl_name [, tbl_name] ... FOR EXPORT
}即通过逐级help的方式即可获得与其主题相关的详细信息。
比较常用的show 命令，通常查看系统变量，状态变量等
mysql> help show;
Name: 'SHOW'
Description:
SHOW has many forms that provide information about databases, tables,
columns, or status information about the server. This section describes
those following:
SHOW {BINARY | MASTER} LOGS
SHOW BINLOG EVENTS [IN 'log_name'] [FROM pos] [LIMIT [offset,] row_count]
SHOW CHARACTER SET [like_or_where]
SHOW COLLATION [like_or_where]
SHOW [FULL] COLUMNS FROM tbl_name [FROM db_name] [like_or_where]
SHOW CREATE DATABASE db_name
SHOW CREATE EVENT event_name
SHOW CREATE FUNCTION func_name
SHOW CREATE PROCEDURE proc_name
SHOW CREATE TABLE tbl_name
SHOW CREATE TRIGGER trigger_name
SHOW CREATE VIEW view_name
SHOW DATABASES [like_or_where]
SHOW ENGINE engine_name {STATUS | MUTEX}
SHOW [STORAGE] ENGINES
SHOW ERRORS [LIMIT [offset,] row_count]
SHOW EVENTS
SHOW FUNCTION CODE func_name
SHOW FUNCTION STATUS [like_or_where]
SHOW GRANTS FOR user
SHOW INDEX FROM tbl_name [FROM db_name]
SHOW MASTER STATUS
SHOW OPEN TABLES [FROM db_name] [like_or_where]
SHOW PLUGINS
SHOW PROCEDURE CODE proc_name
SHOW PROCEDURE STATUS [like_or_where]
SHOW PRIVILEGES
SHOW [FULL] PROCESSLIST
SHOW PROFILE [types] [FOR QUERY n] [OFFSET n] [LIMIT n]
SHOW PROFILES
SHOW RELAYLOG EVENTS [IN 'log_name'] [FROM pos] [LIMIT [offset,] row_count]
SHOW SLAVE HOSTS
SHOW SLAVE STATUS [FOR CHANNEL channel]
SHOW [GLOBAL | SESSION] STATUS [like_or_where]
SHOW TABLE STATUS [FROM db_name] [like_or_where]
SHOW [FULL] TABLES [FROM db_name] [like_or_where]
SHOW TRIGGERS [FROM db_name] [like_or_where]
SHOW [GLOBAL | SESSION] VARIABLES [like_or_where]
SHOW WARNINGS [LIMIT [offset,] row_count]
like_or_where:
LIKE 'pattern'
| WHERE expr
If the syntax for a given SHOW statement includes a LIKE 'pattern'
part, 'pattern' is a string that can contain the SQL % and _ wildcard
characters. The pattern is useful for restricting statement output to
matching values.
Several SHOW statements also accept a WHERE clause that provides more
flexibility in specifying which rows to display. See
http://dev.mysql.com/doc/refman/5.7/en/extended-show.html.
URL: http://dev.mysql.com/doc/refman/5.7/en/show.html以及set的帮助信息：
mysql> help set;
Name: 'SET'
Description:
Syntax:
SET variable_assignment [, variable_assignment] ...
variable_assignment:
user_var_name = expr
| param_name = expr
| local_var_name = expr
| [GLOBAL | SESSION]
system_var_name = expr
| [@@global. | @@session. | @@]
system_var_name = expr
SET syntax for variable assignment enables you to assign values to
different types of variables that affect the operation of the server or
clients:
o System variables. See
http://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html.
System variables also can be set at server startup, as described in
http://dev.mysql.com/doc/refman/5.7/en/using-system-variables.html.
(To display system variable names and values, use the SHOW VARIABLES
statement; see [HELP SHOW VARIABLES].)
o User-defined variables. See
http://dev.mysql.com/doc/refman/5.7/en/user-variables.html.
o Stored procedure and function parameters, and stored program local
variables. See
http://dev.mysql.com/doc/refman/5.7/en/stored-program-variables.html.
URL: http://dev.mysql.com/doc/refman/5.7/en/set-variable.html
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