作者在 2008-03-28 15:57:53 发布以下内容

Select

用途：

从指定表中取出指定的列的数据

语法：

SELECT column_name(s) FROM table_name

解释：

从数据库中选取资料列，并允许从一或多个资料表中，选取一或多个资料列或资料行。SELECT 陈述式的完整语法相当复杂，但主要子句可摘要为：

SELECT select_list
[ INTO new_table ]
FROM table_source
[ WHERE search_condition ]
[ GROUP BY group_by_expression ]
[ HAVING search_condition ]
[ ORDER BY order_expression [ ASC | DESC ] ]

例：

“Persons” 表中的数据有

LastName	FirstName	Address	City
Hansen	Ola	Timoteivn 10	Sandnes
Svendson	Tove	Borgvn 23	Sandnes
Pettersen	Kari	Storgt 20	Stavanger

选出字段名” LastName”、” FirstName” 的数据

SELECT LastName,FirstName FROM Persons

返回结果:

LastName	FirstName
Hansen	Ola
Svendson	Tove
Pettersen	Kari

选出所有字段的数据

SELECT * FROM Persons

返回结果:

LastName	FirstName	Address	City
Hansen	Ola	Timoteivn 10	Sandnes
Svendson	Tove	Borgvn 23	Sandnes
Pettersen	Kari	Storgt 20	Stavanger

Where

用途：

被用来规定一种选择查询的标准

语法：

SELECT column FROM table WHERE column condition value

下面的操作符能被使用在WHERE中：

=,<>,>,<,>=,<=,BETWEEN,LIKE

注意：在某些SQL的版本中不等号< >能被写作为!=

解释：

SELECT语句返回WHERE子句中条件为true的数据

例：

从” Persons”表中选出生活在” Sandnes” 的人

SELECT * FROM Persons WHERE City='Sandnes'

"Persons" 表中的数据有:

LastName	FirstName	Address	City	Year
Hansen	Ola	Timoteivn 10	Sandnes	1951
Svendson	Tove	Borgvn 23	Sandnes	1978
Svendson	Stale	Kaivn 18	Sandnes	1980
Pettersen	Kari	Storgt 20	Stavanger	1960

返回结果:

LastName	FirstName	Address	City	Year
Hansen	Ola	Timoteivn 10	Sandnes	1951
Svendson	Tove	Borgvn 23	Sandnes	1978
Svendson	Stale	Kaivn 18	Sandnes	1980

And & Or

用途：

在WHERE子句中AND和OR被用来连接两个或者更多的条件

解释：

AND在结合两个布尔表达式时，只有在两个表达式都为 TRUE 时才传回 TRUE

OR在结合两个布尔表达式时，只要其中一个条件为 TRUE 时，OR便传回 TRUE

例：

"Persons" 表中的原始数据:

LastName	FirstName	Address	City
Hansen	Ola	Timoteivn 10	Sandnes
Svendson	Tove	Borgvn 23	Sandnes
Svendson	Stephen	Kaivn 18	Sandnes

用AND运算子来查找"Persons" 表中FirstName为”Tove”而且LastName为” Svendson”的数据

SELECT * FROM Persons

WHERE FirstName='Tove'

AND LastName='Svendson'

返回结果:

LastName	FirstName	Address	City
Svendson	Tove	Borgvn 23	Sandnes

用OR运算子来查找"Persons" 表中FirstName为”Tove”或者LastName为” Svendson”的数据

SELECT * FROM Persons

WHERE firstname='Tove'

OR lastname='Svendson'

返回结果:

LastName	FirstName	Address	City
Svendson	Tove	Borgvn 23	Sandnes
Svendson	Stephen	Kaivn 18	Sandnes

你也能结合AND和OR (使用括号形成复杂的表达式),如:

SELECT * FROM Persons WHERE

(FirstName='Tove' OR FirstName='Stephen')

AND LastName='Svendson'

返回结果:

LastName	FirstName	Address	City
Svendson	Tove	Borgvn 23	Sandnes
Svendson	Stephen	Kaivn 18	Sandnes

Between…And

用途：

指定需返回数据的范围

语法：

SELECT column_name FROM table_name

WHERE column_name

BETWEEN value1 AND value2

例：

“Persons”表中的原始数据

LastName	FirstName	Address	City
Hansen	Ola	Timoteivn 10	Sandnes
Nordmann	Anna	Neset 18	Sandnes
Pettersen	Kari	Storgt 20	Stavanger
Svendson	Tove	Borgvn 23	Sandnes

用BETWEEN…AND返回LastName为从”Hansen”到”Pettersen”的数据：

SELECT * FROM Persons WHERE LastName

BETWEEN 'Hansen' AND 'Pettersen'

返回结果:

LastName	FirstName	Address
Hansen	Ola	Timoteivn 10

SQL语法参考

Select

Where

And & Or

"Persons" 表中的原始数据:

Between…And