MySQL帮助文档的使用

帮助文档使用

在 MySQL 使用过程中，可能经常会遇到以下问题：

• 某个操作语法忘记了，需要快速查找。
• 当前版本上，某个字段类型我们想快速知道它的取值范围？
• 当前版本上，都支持哪些函数？希望有例子能快速入门。
• 当前版本上，是否支持某个功能？

对于上面列出的各种问题，我们可能想到的办法是查找 MySQL 的文档。不错，这些问题在 MySQL 官方文档中都可以很清楚地查到，但是却要耗费大量的时间和精力。 所以对于以上问题，最好的解决办法是使用 MySQL 安装后自带的帮助文档，这样在遇到问 题时就可以方便快捷地进行查询。

1. 按照层次看帮助

   如果不知道帮助能够提供些什么，可以用“？contents”命令来显示所有可供查询的的分类， 如下例所示：

   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
      Procedures
      Storage Engines
      Table Maintenance
      Transactions
      User-Defined Functions
      Utility
   

   对于列出的分类，可以使用“? 类别名称”的方式针对用户感兴趣的内容做进一步的查看。 例如，想看看 MySQL 中都支持哪些数据类型，可以执行“? data types”命令：

   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_INCREMENT
      BIGINT
      BINARY
      BIT
      BLOB
      BLOB DATA TYPE
      BOOLEAN
      CHAR
      CHAR BYTE
      DATE
      DATETIME
      DEC
      DECIMAL
      DOUBLE
      DOUBLE PRECISION
      ENUM
      FLOAT
      INT
      INTEGER
      LONGBLOB
      LONGTEXT
      MEDIUMBLOB
      MEDIUMINT
      MEDIUMTEXT
      SET DATA TYPE
      SMALLINT
      TEXT
      TIME
      TIMESTAMP
      TINYBLOB
      TINYINT
      TINYTEXT
      VARBINARY
      VARCHAR
      YEAR DATA TYPE
   
   

   上面列出的此版本支持的所有数据类型，如果想知道int类型的具体介绍，也可以使用上忙的方法，做进一步的查看：

   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: http://dev.mysql.com/doc/refman/5.6/en/numeric-type-overview.html
   

   帮助文档中显示了 int 类型的详细描述。通过这种“？ 类别名称”的方式，就可以一层层 地往下查找用户所关心的主题内容。

2. 快速查阅帮助

   在实际应用当中，如果需要快速查阅某项语法时，可以使用关键字进行快速查询。例如，想 知道 show 命令都能看些什么东西，可以用如下命令:

   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 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/5.6/en/extended-show.html.
   
   URL: http://dev.mysql.com/doc/refman/5.6/en/show.html
   

   例如，如果想参看CREATE TABLE 的语法，可以使用以下命令：

   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_expression
   
   CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
       { LIKE old_tbl_name | (LIKE old_tbl_name) }
   
   create_definition:
       col_name column_definition
     | [CONSTRAINT [symbol]] PRIMARY KEY [index_type] (index_col_name,...)
         [index_option] ...
     | {INDEX|KEY} [index_name] [index_type] (index_col_name,...)
         [index_option] ...
     | [CONSTRAINT [symbol]] UNIQUE [INDEX|KEY]
         [index_name] [index_type] (index_col_name,...)
         [index_option] ...
     | {FULLTEXT|SPATIAL} [INDEX|KEY] [index_name] (index_col_name,...)
         [index_option] ...
     | [CONSTRAINT [symbol]] FOREIGN KEY
         [index_name] (index_col_name,...) reference_definition
     | CHECK (expr)
   
   column_definition:
       data_type [NOT NULL | NULL] [DEFAULT default_value]
         [AUTO_INCREMENT] [UNIQUE [KEY] | [PRIMARY] KEY]
         [COMMENT 'string']
         [COLUMN_FORMAT {FIXED|DYNAMIC|DEFAULT}]
         [STORAGE {DISK|MEMORY|DEFAULT}]
         [reference_definition]
   
   data_type:
       BIT[(length)]
     | TINYINT[(length)] [UNSIGNED] [ZEROFILL]
     | SMALLINT[(length)] [UNSIGNED] [ZEROFILL]
     | MEDIUMINT[(length)] [UNSIGNED] [ZEROFILL]
     | INT[(length)] [UNSIGNED] [ZEROFILL]
     | INTEGER[(length)] [UNSIGNED] [ZEROFILL]
     | BIGINT[(length)] [UNSIGNED] [ZEROFILL]
     | REAL[(length,decimals)] [UNSIGNED] [ZEROFILL]
     | DOUBLE[(length,decimals)] [UNSIGNED] [ZEROFILL]
     | FLOAT[(length,decimals)] [UNSIGNED] [ZEROFILL]
     | DECIMAL[(length[,decimals])] [UNSIGNED] [ZEROFILL]
     | NUMERIC[(length[,decimals])] [UNSIGNED] [ZEROFILL]
     | DATE
     | TIME[(fsp)]
     | TIMESTAMP[(fsp)]
     | DATETIME[(fsp)]
     | YEAR
     | CHAR[(length)] [BINARY]
         [CHARACTER SET charset_name] [COLLATE collation_name]
     | VARCHAR(length) [BINARY]
         [CHARACTER SET charset_name] [COLLATE collation_name]
     | BINARY[(length)]
     | VARBINARY(length)
     | TINYBLOB
     | BLOB
     | MEDIUMBLOB
     | LONGBLOB
     | TINYTEXT [BINARY]
         [CHARACTER SET charset_name] [COLLATE collation_name]
     | TEXT [BINARY]
         [CHARACTER SET charset_name] [COLLATE collation_name]
     | MEDIUMTEXT [BINARY]
         [CHARACTER SET charset_name] [COLLATE collation_name]
     | LONGTEXT [BINARY]
         [CHARACTER SET charset_name] [COLLATE collation_name]
     | ENUM(value1,value2,value3,...)
         [CHARACTER SET charset_name] [COLLATE collation_name]
     | SET(value1,value2,value3,...)
         [CHARACTER SET charset_name] [COLLATE collation_name]
     | spatial_type
   
   index_col_name:
       col_name [(length)] [ASC | DESC]
   
   index_type:
       USING {BTREE | HASH}
   
   index_option:
       KEY_BLOCK_SIZE [=] value
     | index_type
     | WITH PARSER parser_name
     | COMMENT 'string'
   
   reference_definition:
       REFERENCES tbl_name (index_col_name,...)
         [MATCH FULL | MATCH PARTIAL | MATCH SIMPLE]
         [ON DELETE reference_option]
         [ON UPDATE reference_option]
   
   reference_option:
       RESTRICT | CASCADE | SET NULL | NO ACTION | SET DEFAULT
   
   table_options:
       table_option [[,] table_option] ...
   
   table_option:
       ENGINE [=] engine_name
     | AUTO_INCREMENT [=] value
     | AVG_ROW_LENGTH [=] value
     | [DEFAULT] CHARACTER SET [=] charset_name
     | CHECKSUM [=] {0 | 1}
     | [DEFAULT] COLLATE [=] collation_name
     | COMMENT [=] 'string'
     | CONNECTION [=] 'connect_string'
     | DATA DIRECTORY [=] 'absolute path to directory'
     | DELAY_KEY_WRITE [=] {0 | 1}
     | INDEX DIRECTORY [=] 'absolute path to directory'
     | INSERT_METHOD [=] { NO | FIRST | LAST }
     | KEY_BLOCK_SIZE [=] value
     | MAX_ROWS [=] value
     | MIN_ROWS [=] value
     | PACK_KEYS [=] {0 | 1 | DEFAULT}
     | PASSWORD [=] 'string'
     | ROW_FORMAT [=] {DEFAULT|DYNAMIC|FIXED|COMPRESSED|REDUNDANT|COMPACT}
     | STATS_AUTO_RECALC [=] {DEFAULT|0|1}
     | STATS_PERSISTENT [=] {DEFAULT|0|1}
     | STATS_SAMPLE_PAGES [=] value
     | TABLESPACE tablespace_name [STORAGE {DISK|MEMORY|DEFAULT}]
     | UNION [=] (tbl_name[,tbl_name]...)
   
   partition_options:
       PARTITION BY
           { [LINEAR] HASH(expr)
           | [LINEAR] KEY [ALGORITHM={1|2}] (column_list)
           | RANGE{(expr) | COLUMNS(column_list)}
           | LIST{(expr) | COLUMNS(column_list)} }
       [PARTITIONS num]
       [SUBPARTITION BY
           { [LINEAR] HASH(expr)
           | [LINEAR] KEY [ALGORITHM={1|2}] (column_list) }
         [SUBPARTITIONS num]
       ]
       [(partition_definition [, partition_definition] ...)]
   
   partition_definition:
       PARTITION partition_name
           [VALUES
               {LESS THAN {(expr | value_list) | MAXVALUE}
               |
               IN (value_list)}]
           [[STORAGE] ENGINE [=] engine_name]
           [COMMENT [=] 'comment_text' ]
           [DATA DIRECTORY [=] 'data_dir']
           [INDEX DIRECTORY [=] 'index_dir']
           [MAX_ROWS [=] max_number_of_rows]
           [MIN_ROWS [=] min_number_of_rows]
           [TABLESPACE [=] tablespace_name]
           [NODEGROUP [=] node_group_id]
           [(subpartition_definition [, subpartition_definition] ...)]
   
   subpartition_definition:
       SUBPARTITION logical_name
           [[STORAGE] ENGINE [=] engine_name]
           [COMMENT [=] 'comment_text' ]
           [DATA DIRECTORY [=] 'data_dir']
           [INDEX DIRECTORY [=] 'index_dir']
           [MAX_ROWS [=] max_number_of_rows]
           [MIN_ROWS [=] min_number_of_rows]
           [TABLESPACE [=] tablespace_name]
           [NODEGROUP [=] node_group_id]
   
   query_expression:
       SELECT ...   (Some valid select or union statement)
   
   CREATE TABLE creates a table with the given name. You must have the
   CREATE privilege for the table.
   
   By default, tables are created in the default database, using the
   InnoDB storage engine. An error occurs if the table exists, if there is
   no default database, or if the database does not exist.
   
   For information about the physical representation of a table, see
   http://dev.mysql.com/doc/refman/5.6/en/create-table-files.html.
   
   URL: http://dev.mysql.com/doc/refman/5.6/en/create-table.html
   

3. 常用的网络资源

   http://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。

   http://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。

   http://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。

   http://www.mysql.com/news-and-events/newsletter/通常会发布各种关于MySQL的最新消息

小结：

本章简单地介绍了 SQL 语句的基本分类 DML/DDL/DCL，并对每一种分类下的常用 SQL 的用 法进行了举例说明。MySQL 在标准 SQL 的基础上进行了很多扩展，本章对常用的一些语法 做了简单介绍，更详细的说明，读者可以参考 MySQL 的帮助或者官方文档。在本章的最后， 还介绍了用户应如何使用 MySQL 中的帮助文档，以便快速查找各种语法定义