在mysql的使用过程中, 可能经常会遇到以下问题:
- 某个操作语法忘记了, 如何快速查找?
- 如何快速知道当前版本上某个字段类型的取值范围?
- 当前版本都支持哪些函数?希望有例子说明..
- 当前版本是否支持某个功能?
对于上面列出的问题, 我们可能想到的方法是查找MySQL的文档, 这些问题在官方文档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, 最好的解决办法就是使用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.
按层次查看帮助
查看目录
如果不知道能够提供哪些帮助, 可以用? contents命令来显示所有可供查询的分类, 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
查看表字段支持哪些数据类型
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都支持哪些数据类型, 可以执行"? data tyeps"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
上面列出了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, 也可以利用上面的方法, 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/5.5/en/numeric-type-overview.html
查看函数
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 Functions
Comparison operators
Control flow functions
Date and Time Functions
Encryption Functions
Information Functions
Logical operators
Miscellaneous Functions
Numeric Functions
String Functions
再根据列出的目录查看相应函数,比如查看都有什么日期函数
mysql> ? Date and Time Functions
You asked for help about help category: "Date and Time Functions"
For more information, type 'help <item>', where <item> is one of the following
topics:
ADDDATE
ADDTIME
CONVERT_TZ
CURDATE
CURRENT_DATE
CURRENT_TIME
CURRENT_TIMESTAMP
CURTIME
DATE FUNCTION
DATEDIFF
DATE_ADD
DATE_FORMAT
DATE_SUB
DAY
DAYNAME
DAYOFMONTH
DAYOFWEEK
DAYOFYEAR
EXTRACT
FROM_DAYS
FROM_UNIXTIME
GET_FORMAT
HOUR
LAST_DAY
LOCALTIME
LOCALTIMESTAMP
MAKEDATE
MAKETIME
MICROSECOND
MINUTE
MONTH
MONTHNAME
NOW
PERIOD_ADD
PERIOD_DIFF
QUARTER
SECOND
SEC_TO_TIME
STR_TO_DATE
SUBDATE
SUBTIME
SYSDATE
TIME FUNCTION
TIMEDIFF
TIMESTAMP FUNCTION
TIMESTAMPADD
TIMESTAMPDIFF
TIME_FORMAT
TIME_TO_SEC
TO_DAYS
TO_SECONDS
UNIX_TIMESTAMP
UTC_DATE
UTC_TIME
UTC_TIMESTAMP
WEEK
WEEKDAY
WEEKOFYEAR
YEAR
YEARWEEK
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命令都能看到什么东西, 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 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/5.5/en/extended-show.html.
URL: http://dev.mysql.com/doc/refman/5.5/en/show.html
例如, 想查看某个函数CONCAT的使用
mysql> ? concat
Name: 'CONCAT'
Description:
Syntax:
CONCAT(str1,str2,...)
Returns the string that results from concatenating the arguments. May
have one or more arguments. If all arguments are nonbinary strings, the
result is a nonbinary string. If the arguments include any binary
strings, the result is a binary string. A numeric argument is converted
to its equivalent string form. This is a nonbinary string as of MySQL
5.5.3. Before 5.5.3, it is a binary string; to to avoid that and
produce a nonbinary string, you can use an explicit type cast, as in
this example:
SELECT CONCAT(CAST(int_col AS CHAR), char_col);
CONCAT() returns NULL if any argument is NULL.
URL: http://dev.mysql.com/doc/refman/5.5/en/string-functions.html
Examples:
mysql> SELECT CONCAT('My', 'S', 'QL');
-> 'MySQL'
mysql> SELECT CONCAT('My', NULL, 'QL');
-> NULL
mysql> SELECT CONCAT(14.3);
-> '14.3'
又例如, 如果想查看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]
Or:
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
[(create_definition,...)]
[table_options]
[partition_options]
select_statement
Or:
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
{ LIKE old_tbl_name | (LIKE old_tbl_name) }
......
再举一个例子吧, 比如想查看创建用户GRANT语法怎么写
mysql> ? grant
Name: 'GRANT'
Description:
Syntax:
GRANT
priv_type [(column_list)]
[, priv_type [(column_list)]] ...
ON [object_type] priv_level
TO user_specification [, user_specification] ...
[REQUIRE {NONE | ssl_option [[AND] ssl_option] ...}]
[WITH with_option ...]
GRANT PROXY ON user_specification
TO user_specification [, user_specification] ...
[WITH GRANT OPTION]
object_type:
TABLE
| FUNCTION
| PROCEDURE
......
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.