一、查询帮助文档

输入命令 ? contents 或者 help contents 来显示所有可供查询的分类：

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 ManagementAdministrationCompound StatementsContentsData DefinitionData ManipulationData TypesFunctionsGeographic FeaturesHelp MetadataLanguage StructurePluginsProceduresStorage EnginesTable MaintenanceTransactionsUser-Defined FunctionsUtility

接着，你可以继续查询相关的分类，例如查看数据库支持的数据类型，可以输入命令 ? data types：

mysql> ? data types;
You asked for help about help category: "Data Types"
For more information, type 'help <item>', where <item> is one of the following
topics:AUTO_INCREMENTBIGINTBINARYBITBLOBBLOB DATA TYPEBOOLEANCHARCHAR BYTEDATEDATETIMEDECDECIMALDOUBLEDOUBLE PRECISIONENUMFLOATINTINTEGERLONGBLOBLONGTEXTMEDIUMBLOBMEDIUMINTMEDIUMTEXTSET DATA TYPESMALLINTTEXTTIMETIMESTAMPTINYBLOBTINYINTTINYTEXTVARBINARYVARCHARYEAR DATA TYPE

如果想知道 int 类型的具体介绍，可以输入命令 ? int：

mysql> ? int
Name: 'INT'
Description:
INT[(M)] [UNSIGNED] [ZEROFILL]A normal-size integer. The signed range is -2147483648 to 2147483647.
The unsigned range is 0 to 4294967295.URL: https://dev.mysql.com/doc/refman/5.6/en/numeric-type-overview.html

查看数据库的函数分类，输入命令 ? functions：

mysql> ? functions;
You asked for help about help category: "Functions"
For more information, type 'help <item>', where <item> is one of the following
categories:Bit FunctionsComparison OperatorsControl Flow FunctionsDate and Time FunctionsEncryption FunctionsGROUP BY Functions and ModifiersInformation FunctionsLocking FunctionsLogical OperatorsMiscellaneous FunctionsNumeric FunctionsSpatial FunctionsString Functions

查看某个具体函数的使用说明，例如查看ifnull函数的使用说明，输入命令 ? ifnull：

mysql> ? ifnull;
Name: 'IFNULL'
Description:
Syntax:
IFNULL(expr1,expr2)If expr1 is not NULL, IFNULL() returns expr1; otherwise it returns
expr2.URL: https://dev.mysql.com/doc/refman/5.6/en/control-flow-functions.htmlExamples:
mysql> SELECT IFNULL(1,0);-> 1
mysql> SELECT IFNULL(NULL,10);-> 10
mysql> SELECT IFNULL(1/0,10);-> 10
mysql> SELECT IFNULL(1/0,'yes');-> 'yes'

查看数据库命令的详细说明，例如查看命令 show 的使用说明，输入命令 ? show：

mysql> ? 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 AUTHORS
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 CONTRIBUTORS
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
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 exprIf 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
https://dev.mysql.com/doc/refman/5.6/en/extended-show.html.URL: https://dev.mysql.com/doc/refman/5.6/en/show.html

如果想查看 create table 的语法, 可以使用以下命令 create table：

mysql> ? create table;
Name: 'CREATE TABLE'
Description:
Syntax:
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name(create_definition,...)[table_options][partition_options]CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name[(create_definition,...)][table_options][partition_options][IGNORE | REPLACE][AS] query_expressionCREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name{ LIKE old_tbl_name | (LIKE old_tbl_name) }create_definition:col_name column_definition| {INDEX|KEY} [index_name] [index_type] (key_part,...)[index_option] ...| {FULLTEXT|SPATIAL} [INDEX|KEY] [index_name] (key_part,...)[index_option] ...

二、MySQL 相关资源网址

https://dev.mysql.com/downloads/：是MySQL的官方网站, 可以下载到各个版本的MySQL以及相关客户端开发工具等.
https://dev.mysql.com/doc/：提供了目前最权威的MySQL数据库及工具的在线手册
https://bugs.mysql.com/：这里可以查看到MySQL已经发布的bug列表, 或者向MySQL提交bug报告
https://www.mysql.com/news-and-events/newsletter/：通常会发布各种关于MySQL的最新消息.