mysql有很完善的帮助文档，在mysql命令行下可以通过？ 或者help 加上命令可以查看改命令的帮助信息，

我们查下几个常用的help命令

第一层帮助信息：

 ？ contents;

mysql> ? 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
   Table Maintenance
   Transactions
   User-Defined Functions
   Utility

再查看具体每一层的帮助信息

  mysql> ? 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:
   CREATE USER
   DROP USER
   GRANT
   RENAME USER
   REVOKE
   SET PASSWORD

mysql> ? 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
   CHANGE MASTER TO
   DEALLOCATE PREPARE
   EXECUTE STATEMENT
   FLUSH
   FLUSH QUERY CACHE
   HELP COMMAND
   KILL
   LOAD INDEX
   PREPARE
   PURGE BINARY LOGS
   RESET
   RESET MASTER
   RESET SLAVE
   SET
   SET GLOBAL SQL_SLAVE_SKIP_COUNTER
   SET SQL_LOG_BIN
   SHOW
   SHOW AUTHORS
   SHOW BINARY LOGS
   SHOW BINLOG EVENTS
   SHOW CHARACTER SET
   SHOW COLLATION
   SHOW COLUMNS
   SHOW CONTRIBUTORS
   SHOW CREATE DATABASE
   SHOW CREATE EVENT
   SHOW CREATE FUNCTION
   SHOW CREATE PROCEDURE
   SHOW CREATE TABLE
   SHOW CREATE TRIGGER
   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
   START SLAVE
   STOP SLAVE

mysql> ?  Compound Statements;
You asked for help about help category: "Compound Statements"
For more information, type 'help &