SQL Server基本命令

操作表：

Student (S#,Sname, Ssex,Sage,D#,Sclass)

SC(S#,C#,Score)

Course(C#,Cname,Chours,Credit,T#)

Teacher(T#,Tname,D#,Salary)

Dept(D#,Dname,Dean)

create：创建数据库或表

create database SCT    --创建数据库

create table SC(       --创建表
S# char(8),
C# char(3),
Score int
)

select：选取数据

select Sname from Student

select * from Student    -- 显示Student表中所有列的信息

distinct：去重

select distinct Sname from Student

where：按条件选择

select Sname from Student
where Ssex = '女'

and 和 or

select Sname from Student
where Ssex = '女' and Sage < 20

select Sname from Student
where Ssex = '女' or Sage < 20

odrder by：对结果进行排序

select S#, Sname from Student
order by Sage asc       -- 按升序进行排序，降序desc

insert：插入

insert into Student values('98030101','张三','男',20，'03','980301')

insert into Student(S#, Sname, Ssex) values('98030102','张四','男')

updata：更新

update Student
set D# = '05',Ssex = '女' where Sname = '赵四'

delete：删除

delete from Student
where Sname = '张三'

delete * from Student    -- 删除Student中所有行

like：模糊查询

select S#, Sname from Student
where Sname like '张%'    -- 寻找叫张某某的学生，'%'匹配零个或多个字符

select S#, Sname from Student
where Sname like '张_'    -- 寻找叫张某的同学，'_'匹配单个字符

select S#, Sname from Student
where Sname like '张\%'    -- 寻找叫张%的同学，'\'表转义字符

select S#, Sname from Student
where Sname like '[张]%'    -- 寻找以张开头的同学

select S#, Sname from Student
where Sname like '[^张]%'    -- 寻找不是以张开头的同学

in：允许在 where 子句中规定多个值

select distinct S# from SC    -- 列举学过001号课程和002号课程同学的学号
where C# in ('001','002');

as：别名

select Sname as 姓名 from Student

inner join：内连接

select * from Student
inner join SC on Student.S# = SC.S#

left join：左连接

select * from Student
left join SC on Student.S# = SC.S#

right join：右连接

select * from Student
right join SC on Student.S# = SC.S#

full join：全连接

select * from Student
full join SC on Student.S# = SC.S#

Union：并

select Sname from Student, SC where Student.S# = SC.S# and C# = '001'
union
select Sname from Student, SC where Student.S# = SC.S# and C# = '002'

-- Union后面加all 列出所有值（包括重复）

select into：批量复制

select Student.S#, Sname, Score into StudentBackup
from Student,SC
where Ssex = '女' and SC.S# = Student.S#

constraint：完整性约束

-- 列约束
create table tablename(colname datatype，    -- colname列的数据类型datatype

not null    -- 列值非空,表示若不向该字段添加值，则无法插入或更新新纪录

unique    -- 列值唯一，每个表可以有多个

primary key    -- 列为主键，每个表只能有一个，包含非空唯一特性

constraint constraintname    -- 约束命名为constraintname

check(search_cond)    -- 列值满足条件search_cond，条件只能使用列当前值

references tablename (colname) on delete cascade | set null) -- 引用tablename的列colname的值，若引用表的某项被删除，对应本表的对应项被删除或者更新为null

-- 表约束
create table tablename(colname,colname,...),

constraint constraintname    -- 为约束名

unique(colname, colname,...)    -- 几列值组合在一起是唯一

primary key(colname, colname, ...)    -- 几列联合为主键

check(search_condition)    -- 元组多列值共同满足的条件，条件中只能使用同一元组的不同列当前值

foreign key(colname, colname,...)
reference tablename(colname, colname, ...)
on delete cascade | set null    -- 引用另一个表tablename的若干列的值作为外键

drop：删除

drop table Student    -- 删除表
drop database SCT     -- 删除数据库
truncate table Student    -- 只删除表的内容

alter：修改

alter table Student    -- 增加列
add Sheight float

alter table Student    -- 删除列
drop column Sheight

alter table Student
alter column Sheight int    -- 修改列的属性

view：视图

create view test as        -- 创建视图
select S#, Sname from Student

select * from test        -- 查询视图

select Sname from test    -- 在视图的基础上添加条件

drop view test            -- 撤销视图

group by：

select sum(Score) from SC        -- 每个学生的总成绩
group by S#

select sum(Score) from SC        -- 每门课程的总成绩
group by C#

having：

Select S#, Avg(Score) from SC    -- 有一门以上及格的同学的及格科目的平均成绩
where Score > 60
group by S# having Count(*) > 1


select S#, Avg(Score) from SC        -- 有一门以上及格的同学的所有科目的平均成绩
where S# in ( select S# from SC
where Score > 60
group by S# having Count(*) > 1)
group by S#;

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