sql基本语句整理

//sql基本语句整理

//创建数据库

CREATE DATABASE database_name;

//删除数据库

DROP DATABASE database_name;

//创建模式

CREATE SCHEMA name_of_schema AUTHORIZATION name_of_user;

//删除模式

DROP SCHEMA name_of_schema CASCADE; //连级删除,包括所有对象

DROP SCHEMA name_of_schema RESTRICT; //若有下属对象,拒绝执行删除操作

//创建表

CREATE TABLE name_of_table

(

name_of_column1 column_datatype,

name_of_column2 column_datatype,

name_of_column3 column_datatype

);

//例子

CREATE TABLE Train_Times

(

start_location varchar(75),

destination varchar(75),

departs time,

arrives time

);

//基本表的修改

ALTER TABLE name_of_table

ADD name_of_newcolumn data_type condition;

DROP condition;

ALTER COLUMN name_of_column data_type condition;

//删除基本表

DROP TABLE name_of_table CASCADE; //删除都有依赖对象

DROP TABLE name_of_table RESTRICT; //有依赖对象则拒绝删除

DROP TABLE Student CASCADE;

//数据类型

CHAR(n) // 长度 为n的定长字符串

VARCHAR(n) // 最大长度为n的变长字符串

INT/INTEGER //长整数

SMALLINT //短整数

NUMERIC(p,d) //定点数,p位数字,d位小数

REAL //机器精度的浮点数

Double Precision //机器长度的双精度浮点数

FLOAT(n) //浮点数,精度至少为n

DATA //日期 YYYY-MM-DD

TIME //时间 HH:MM:SS

//插入新数据

INSERT INTO

table_name (column_name1,column_name2,column_name3,....)

INTO

VALUES(data_value1,data_value2,data_value3,....);

//显示表中所有数据

SELECT *

FROM table_name

CREATE TABLE MemberDatils //

(

MemberId integer,

FirstName varchar(50),

LastName varchar(50),

DateOfBirth data,

Street varchar(100),

City varchar(75),

_State varchar(75),

ZipCode varchar(12),

Email varchar(200),

DateOfJoining date

);

INSERT INTO

MemberDatils

VALUES

(

1,

'Katie',

'Smith',

'1977-01-09',

'Main Road',

'Townsville',

'Stateside',

'123456',

'kate@mail.com',

'2004-02-23'

);

CREATE TABLE Category

(

CategoryID integer,

Category varchar(190)

);

INSERT INTO

Category(categoryID,Category)

VALUES(6,'historical');

//更新数据

UPDATE table_name

SET column_name=data_value

WHERE condition

UPDATE MemberDetails

SET

Street='45 upper road',

city='new town',

_state='new state',

ZipCode='99112'

WHERE MemberID=4;

//WHERE子句,用于查询和更新时作为条件

//<>表示不等于

//逻辑运算符AND和OR

//相当于C++中的&&和||

UPDATE MemberDetils

SET _State='mega state'

WHERE

_State='small state'

OR

_State='stateside';

UPDATE Location

SET _State='Mega State'

WHERE

_State='small state'

OR

_State='stateside';

//删除数据

DELETE FROM MemberDetails //删除表中所有记录

DELETE FROM MemberDetails //可以用WHERE指定条件

WHERE MemberID=3;

//提取信息与查询

SELECT column1,column2,columnx

FROM table_name;

//

SELECT MemberID,FirstName

FROM MemberDetails;

//用*取代所有列

SELECT *

FROM Location;

//尽量不使用所有列,影像处理速度浪费内存

//如果只想知道一个记录中的唯一值,可以用DISTINCT

SELECT DISTINCT City

FROM MemberDetails;

//city只会出现唯一值

//使用别名

SELECT sname NAME,yearOfBirth BIRTH,2004-sage BIRTHDAY,LOWER(sdept) DEPARTMENT

FROM Student;

SELECT LastName AS Surname

FROM MemberDetails;

//利用WHERE过滤子结果

SELECT FirstName + ' ' + LastName AS [FULL NAME]

FROM MemberDetails

WHERE City='Big City';

//运算符优先级

//圆括号()

//NOT

//AND

//ALL,ANY,BETWEEN,IN,LIKE,OR,SOME

//尽量使用园括号改变优先级

//基于true的条件 被过滤

SELECT FirstName

FROM MemberDetails

WHERE NOT State='Golden State';

//

SELECT FirstName

FROM MemberDetails

WHERE State<> 'Golden State';

//BETWEEN 用于指定一个范围

//这个范围位于两个值之间

SELECT FilitiName,Rating

FROM Films

WHERE Rating BETWEEN 3 AND 5;

//LIKE 运算符

//用于字符串匹配

SELECT LastName

FROM MemberDetails

WHERE LastName LIKE 'j%';

//在某些数据库中,LIKE区分大小写如oracle

//%匹配一个或多个字符

//_匹配一个字符

SELECT LastName

FROM MemberDetails

WHERE LastName LIKE 'D__s';

//LIKE经常和NOT LIKE 合用

//IN运算符

SELECT City

FROM MemberDetails

WHERE

City IN ('TOWNSVILL','windy village','Dover','Big City');

SELECT FolmName,YearReleased,Rating

FROM Films

WHERE

YearReleased IN (1967,1977,1987)

AND

Rating IN (4,5);

//利用ORDER BY排序结果

//默认升序

SELECT YearReleased

FROM Films

ORDER BY YearReleased;

ORDER BY YearReleased DESC;

//若有WHERE ,ORDER BY要置于WHERE的后面

//BETWEEN '2005-01-01' AND '2005-02-03'

//从多个表选择数据

SELECT FileName,YearReleased,Rating

FROM Films INNER JOIN Category

ON Films.CategoryId = Category.CategoryId

WHERE Category.CategoryId =6;

SELECT FileName,YearReleased,Rating

FROM Films,Category

ON Films.CategoryId = CategoryId.CategoryId

WHERE Category.CategoryID=6;

//约束

//NOT NULL

CREATE TABLE MyTable

(

Column1 int NOT NULL,

Column2 varchar(20),

Column3 varchar(12) NOT NULL

);

ALTER TABLE MyTable

MODIFY Column2 varchar(20) NOT NULL;

//UNIQUE

//防止特定列中两个值一样

//保证特定列数据唯一性

CREATE TABLE MyTable

(

Column1 int UNIQUE,

Column2 varchar(20) UNIQUE,

Column3 varchar(12) UNIQUE

);

//CHECK约束

///检查每一个输入到记录中的值,若为假,则违反约束,并不输入到表中.

CREATE TABLE NamesAges

(

Name varchar(50),

Age int CHECK(Age>0)

);

INSERT INTO

NamesAges(Name,Age)

VALUES('jim',30);

//主键约束,每个表都应当有一个主键

CREATE TABLE HolidayBookings

(

CustomerId int PRIMARY KEY,

BookingId int,

Destination varchar(50)

);

//IBM DB2中,主键列必须为NOT NULL

CREATE TABLE HolidayBookings

(

CustomerId int NOT NULL PRIMARY KEY,

BookingId int,

Destination varchar(50)

);

//

CREATE TABLE HolidayBookings

(

CustomerId int NOT NULL,

BookingId int NOT NULL,

Destination varchar(50),

PRIMARY KEY(CustomerId,BookingId)

);

//外键约束

//外键是访问另一个表中的主键的列

FOREIGN KEY (NAME_OF_COLUMN) REFERENCES NAME_OF_TABLE(NAME_OF_PRIMARYCOLUMN);

CREATE TABLE SC

(

Sno CHAR(9),

Cno CHAR(4),

PRIMARY KEY (Sno,Cno),

FOREIGN KEY (Sno) REFERENCES Student(Sno),

FOREIGN KEY (Cno) REFERENCES Course(Cno)

);

//索引

CREATE INDEX NAME_OF_INDEX

ON NAME_OF_TABLE(COLUMN1 ASC,COLUMN2 DESC,...)

CREATE UNIQUE INDEX NAME_OF_INDEX //一个索引对应唯一的记录

CREATE CLUSTER INDEX NAME_OF_INDEX //创建群簇索引,经常更新的数据不宜采用

//删除索引

DROP INDEX name_of_table.index_name;

//设计好的数据库的技巧

//不要设计仅满足普通情况的情形,要覆盖所有可能发生的情况

//为表和字段选择有意义的名称

//尽量使名称简单

//命名和数据类型要一致

//先在纸上分析需求

//仔细选择主键

//创建一个索引,加快搜索速度

//添加一个多列索引

//避免使用保留字作为表名或字段名

//考虑储存空间

//转载请注明出处