SQL 语法手册
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 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 https://www.wendangku.net/doc/7117150061.html,, Orders.Product
FROM Employees, Orders
WHERE Employees.ID = Orders.ID
返回结果:
Name Product
Hansen, Ola Printer
Svendson,
Table
Stephen
Svendson,
Chair
Stephen
或者你也可以用JOIN关键字来完成上面的操作:
SELECT https://www.wendangku.net/doc/7117150061.html,, 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 https://www.wendangku.net/doc/7117150061.html,, Orders.Product
FROM Employees
LEFT JOIN Orders
ON Employees.ID = Orders.ID
返回结果:
Name Product
Hansen, Ola Printer
Svendson, Tove
Svendson,
Table
Stephen
Svendson,
Chair
Stephen
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 https://www.wendangku.net/doc/7117150061.html,, Orders.Product
FROM Employees
RIGHT JOIN Orders
ON Employees.ID = Orders.ID
返回结果:
Name Product
Hansen, Ola Printer
Svendson,
Table
Stephen
Svendson,
Chair
Stephen
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