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SQL的详细语法介绍――对于学习数据库最_sqlserver

sqlserver 搞代码 3年前 (2018-06-16) 91次浏览 已收录 0个评论

Select
用途:

 从指定表中取出指定的列的数据

语法:

http://www.gaodaima.com/35858.htmlSQL的详细语法介绍――对于学习数据库最_sqlserver

 

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

City

Hansen

Ola

Timoteivn 10

Sandnes

Nordmann

Anna

Neset 18

Sandnes

Pettersen

Kari

Storgt 20

Stavanger

 

为了显示指定范围之外的数据,也可以用NOT操作符:

SELECT * FROM Persons WHERE LastName

NOT BETWEEN ‘Hansen’ AND ‘Pettersen’

返回结果:

LastName

FirstName

Address

City

Svendson

Tove

Borgvn 23

Sandnes

 

 
Distinct
用途:

 DISTINCT关键字被用作返回唯一的值

语法:

SELECT DISTINCT column-name(s) FROM table-name

解释:

 当column-name(s)中存在重复的值时,返回结果仅留下一个

例:

“Orders”表中的原始数据

Company

OrderNumber

Sega

3412

W3Schools

2312

Trio

4678

W3Schools

6798

用DISTINCT关键字返回Company字段中唯一的值:

SELECT DISTINCT Company FROM Orders

返回结果:

Company

Sega

W3Schools

Trio

 

 
Order by
用途:

指定结果集的排序

语法:

SELECT column-name(s) FROM table-name ORDER BY { order_by_expression [ ASC | DESC ] }

解释:

 指定结果集的排序,可以按照ASC(递增方式排序,从最低值到最高值)或者DESC(递减方式排序,从最高值到最低值)的方式进行排序,默认的方式是ASC

例:

“Orders”表中的原始数据:

Company

OrderNumber

Sega

3412

ABC Shop

5678

W3Schools

2312

W3Schools

6798

按照Company字段的升序方式返回结果集:

SELECT Company, OrderNumber FROM Orders

ORDER BY Company

返回结果:

Company

OrderNumber

ABC Shop 

5678

Sega

3412

W3Schools

6798

W3Schools

2312

按照Company字段的降序方式返回结果集:

SELECT Company, OrderNumber FROM Orders

ORDER BY Company DESC

返回结果:

Company

OrderNumber

W3Schools

6798

W3Schools

2312

Sega

3412

ABC Shop

5678

 

 
Group by
用途:

对结果集进行分组,常与汇总函数一起使用。

语法:

SELECT column,SUM(column) FROM table GROUP BY column

例:

“Sales”表中的原始数据:

Company

Amount

W3Schools

5500

IBM

4500

W3Schools

7100

按照Company字段进行分组,求出每个Company的Amout的合计:

SELECT Company,SUM(Amount) FROM Sales

GROUP BY Company

返回结果:

Company

SUM(Amount)

W3Schools

12600

IBM

4500

 

 
Having
用途:

指定群组或汇总的搜寻条件。

语法:

SELECT column,SUM(column) FROM table

GROUP BY column

HAVING SUM(column) condition value

解释:

HAVING 通常与 GROUP BY 子句同时使用。不使用 GROUP BY 时,HAVING 则与 WHERE 子句功能相似。

例:

“Sales”表中的原始数据:

Company

Amount

W3Schools

5500

IBM

4500

W3Schools

7100

按照Company字段进行分组,求出每个Company的Amout的合计在10000以上的数据:

SELECT Company,SUM(Amount) FROM Sales

GROUP BY Company HAVING SUM(Amount)>10000

返回结果:

Company

SUM(Amount)

W3Schools

12600

 

 
Join
用途:

当你要从两个或者以上的表中选取结果集时,你就会用到JOIN。

例:

“Employees”表中的数据如下,(其中ID为主键):

ID

Name

01

Hansen, Ola

02

Svendson, Tove

03

Svendson, Stephen

04

Pettersen, Kari

“Orders”表中的数据如下:

ID

Product

01

Printer

03

Table

03

Chair

用Employees的ID和Orders的ID相关联选取数据:

SELECT Employees.Name, Orders.Product

FROM Employees, Orders

WHERE Employees.ID = Orders.ID

返回结果:

Name

Product

Hansen, Ola

Printer

Svendson, Stephen

Table

Svendson, Stephen

Chair

或者你也可以用JOIN关键字来完成上面的操作:

SELECT Employees.Name, Orders.Product

FROM Employees

INNER JOIN Orders

ON Employees.ID = Orders.ID

INNER JOIN的语法:

SELECT field1, field2, field3

FROM first_table

INNER JOIN second_table

ON first_table.keyfield = second_table.foreign_keyfield

解释:

       INNER JOIN返回的结果集是两个表中所有相匹配的数据。

 

LEFT JOIN的语法:

SELECT field1, field2, field3

FROM first_table

LEFT JOIN second_table

ON first_table.keyfield = second_table.foreign_keyfield

用”Employees”表去左外联结”Orders”表去找出相关数据:

SELECT Employees.Name, Orders.Product

FROM Employees

LEFT JOIN Orders

ON Employees.ID = Orders.ID

返回结果:

Name

Product

Hansen, Ola

Printer

Svendson, Tove

 

Svendson, Stephen

Table

Svendson, Stephen

Chair

Pettersen, Kari

 

解释:

       LEFT JOIN返回”first_table”中所有的行尽管在” second_table”中没有相匹配的数据。

 

RIGHT JOIN的语法:

SELECT field1, field2, field3

FROM first_table

RIGHT JOIN second_table

ON first_table.keyfield = second_table.foreign_keyfield

用”Employees”表去右外联结”Orders”表去找出相关数据:

SELECT Employees.Name, Orders.Product

FROM Employees

RIGHT JOIN Orders

ON Employees.ID = Orders.ID

返回结果:

Name

Product

Hansen, Ola

Printer

Svendson, Stephen

Table

Svendson, Stephen

Chair

解释:

       RIGHT JOIN返回” second_table”中所有的行尽管在”first_table”中没有相匹配的数据。

 
Alias
用途:

可用在表、结果集或者列上,为它们取一个逻辑名称

语法:

给列取别名:

SELECT column AS column_alias FROM table

       给表取别名:

SELECT column FROM table AS table_alias

例:

“Persons”表中的原始数据:

LastName

FirstName

Address

City

Hansen

Ola

Timoteivn 10

Sandnes

Svendson

Tove

Borgvn 23

Sandnes

Pettersen

Kari

Storgt 20

Stavanger

运行下面的SQL:

SELECT LastName AS Family, FirstName AS Name

FROM Persons

返回结果:

Family

Name

Hansen

Ola

Svendson

Tove

Pettersen

Kari

运行下面的SQL:

SELECT LastName, FirstName

FROM Persons AS Employees

返回结果:

Employees中的数据有:

LastName

FirstName

Hansen

Ola

Svendson

Tove

Pettersen

Kari

 

 
Insert Into
用途:

       在表中插入新行

语法:

       插入一行数据

INSERT INTO table_name

VALUES (value1, value2,….)

       插入一行数据在指定的字段上

INSERT INTO table_name (column1, column2,…)

VALUES (value1, value2,….)  

例:

“Persons”表中的原始数据:

LastName

FirstName

Address

City

Pettersen

Kari

Storgt 20

Stavanger

运行下面的SQL插入一行数据:

INSERT INTO Persons 

VALUES (‘Hetland’, ‘Camilla’, ‘Hagabakka 24’, ‘Sandnes’)

插入后”Persons”表中的数据为:

LastName

FirstName

Address

City

Pettersen

Kari

Storgt 20

Stavanger

Hetland

Camilla

Hagabakka 24

Sandnes

运行下面的SQL插入一行数据在指定的字段上:

INSERT INTO Persons (LastName, Address)

VALUES (‘Rasmussen’, ‘Storgt 67’)

插入后”Persons”表中的数据为:

LastName

FirstName

Address

City

Pettersen

Kari

Storgt 20

Stavanger

Hetland

Camilla

Hagabakka 24

Sandnes

Rasmussen

 

Storgt 67

 

 

 
Update
用途:

       更新表中原有数据

语法:

UPDATE table_name SET column_name = new_value

WHERE column_name = some_value

例:

“Person”表中的原始数据:

LastName

FirstName

Address

City

Nilsen

Fred

Kirkegt 56

Stavanger

Rasmussen

 

Storgt 67

 

运行下面的SQL将Person表中LastName字段为”Rasmussen”的FirstName更新为”Nina”:

UPDATE Person SET FirstName = ‘Nina’

WHERE LastName = ‘Rasmussen’

更新后”Person”表中的数据为:

LastName

FirstName

Address

City

Nilsen

Fred

Kirkegt 56

Stavanger

Rasmussen

Nina

Storgt 67

 

同样的,用UPDATE语句也可以同时更新多个字段:

UPDATE Person

SET Address = ‘Stien 12’, City = ‘Stavanger’

WHERE LastName = ‘Rasmussen’

更新后”Person”表中的数据为:

LastName

FirstName

Address

City

Nilsen

Fred

Kirkegt 56

Stavanger

Rasmussen

Nina

Stien 12

Stavanger

 

 
Delete
用途:

       删除表中的数据

语法:

DELETE FROM table_name WHERE column_name = some_value

例:

“Person”表中的原始数据:

LastName

FirstName

Address

City

Nilsen

Fred

Kirkegt 56

Stavanger

Rasmussen

Nina

Stien 12

Stavanger

删除Person表中LastName为”Rasmussen”的数据:

DELETE FROM Person WHERE LastName = ‘Rasmussen’

执行删除语句后”Person”表中的数据为:

LastName

FirstName

Address

City

Nilsen

Fred

Kirkegt 56

Stavanger

 

 
Create Table
用途:

       建立新的资料表。

语法:

CREATE TABLE table_name

(

column_name1 data_type,

column_name2 data_type,

…….

)

例:

创建一张叫“Person”的表,该表有4个字段”LastName”, “FirstName”, “Address”, “Age”:

CREATE TABLE Person 

(

LastName varchar,

FirstName varchar,

Address varchar,

Age int

)

如果想指定字段的最大存储长度,你可以这样:

CREATE TABLE Person 

(

LastName varchar(30),

FirstName varchar(30),

Address varchar(120),

Age int(3) 

)

下表中列出了在SQL的一些数据类型:

Data Type

Description

integer(size)
int(size)
smallint(size)
tinyint(size)

Hold integers only. The maximum number of digits are specified in parenthesis.

decimal(size,d)
numeric(size,d)

Hold numbers with fractions. The maximum number of digits are specified in “size”. The maximum number of digits to the right of the decimal is specified in “d”.

char(size)

Holds a fixed length string (can contain letters, numbers, and special characters). The fixed size is specified in parenthesis.

varchar(size)

Holds a variable length string (can contain letters, numbers, and special characters). The maximum size is specified in parenthesis.

date(yyyymmdd)

Holds a date

 

 
Alter Table
用途:

       在已经存在的表中增加后者移除字段

语法:

ALTER TABLE table_name

ADD column_name datatype

ALTER TABLE table_name

DROP COLUMN column_name

注意:某些数据库管理系统不允许移除表中的字段

 

例:

“Person”表中的原始数据:

LastName

FirstName

Address

Pettersen

Kari

Storgt 20

 

在Person表中增加一个名为City的字段:

ALTER TABLE Person ADD City varchar(30)

增加后表中数据如下:

LastName

FirstName

Address

City

Pettersen

Kari

Storgt 20

 

 

移除Person表中原有的Address字段:

ALTER TABLE Person DROP COLUMN Address

移除后表中数据如下:

LastName

FirstName

City

Pettersen

Kari

 

 

 
Drop Table
用途:

       在数据库中移除一个数据表定义及该数据表中的所有资料、索引、触发程序、条件约束及权限指定。

语法:

DROP TABLE table_name

 

 
Create Database
用途:

       建立新的数据库.

语法:

CREATE DATABASE database_name

 

 
Drop Database
用途:

       移除原有的数据库

语法:

DROP DATABASE database_name

 

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