sql 创建表、删除表 增加字段 删除字段操作

\\\'添加字段通用函数
Sub AddColumn(TableName,ColumnName,ColumnType)
Conn.Execute(\"Alter Table \"&TableName&\" Add \"&ColumnName&\" \"&ColumnType&\"\")
End Sub
删除约束：
ALTER TABLE [表名] DROP CONSTRAINT 约束名
新建默认值
ALTER TABLE [表名] ADD CONSTRAINT 默认值名 DEFAULT \'\' FOR [字段名]
删除默认值
ALTER TABLE [表名] DROP CONSTRAINT 默认值名
from S
where sname='S5');
(5)
seleCt sname
from S
where sdept='英语'and sex='男';
(6)
seleCt SC.sno,avg(grade) as average
from S,SC
where S.sno=SC.sno
)
create table C
(
cno char(8),
cname char(16),
credit int,
constraint PK_C primary key (cno),
constraint CK_credit check (credit>=0)
)
create table SC
下面是Sql Server 和 Access 操作数据库结构的常用Sql，希望对你有所帮助。
新建表：
create table [表名]
(
[自动编号字段] int IDENTITY (1,1) PRIMARY KEY ,
[字段1] nVarChar(50) default \'默认值\' null ,
Cpno int not null,
Ccredit tinyint not null)
create table sc(
Sno int not null,
Cno int not null,
Grade tinyint not null
foreign key(Sno)references student(Sno)
Sname char(10)not null,
Ssex bit not null,
Sage tinyint not null,
Sdept char(20) not null)
create table course(
Cno int not null primary key,
Cname char(20)not null,
set rs=conn.execute(sql)
response.write rs(\"dida\")\'返回一个数值，0代表没有，1代表存在
判断表的存在:
select * from sysobjects where id = object_id(N\'[dbo].[tablename]\') and OBJECTPROPERTY(id, N\'IsUserTable\') = 1
[字段2] ntext null ,
[字段3] datetime,
[字段4] money null ,
[字段5] int default 0,
[字段6] Decimal (12,4) default 0,
[字段7] image null ,
)
删除表：
Drop table [表名]
\\\'更改字段通用函数
Sub ModColumn(TableName,ColumnName,ColumnType)
Conn.Execute(\"Alter Table \"&TableName&\" Alter Column \"&ColumnName&\" \"&ColumnType&\"\")
插入数据：
INSERT INTO [表名] (字段1,字段2) VALUES (100,\'\')
删除数据：
DELETE FROM [表名] WHERE [字段名]>100
更新数据：
UPDATE [表名] SET [字段1] = 200,[字段2] = \'\' WHERE [字段三] = \'HAIWA\'
End Sub
\\\'检查表是否存在
sql=\"select count(*) as dida from sysobjects where id = object_id(N\'[所有者].[表名]\') and OBJECTPROPERTY(id, N\'IsUserTable\') = 1\"
where SCZ.Sno=SCX.Sno and o=o));
(12)
select top 3 Cno as 课程号, Sno
from SC
where Cno=1
order by Grade desc;
create database stu
重命名表：(Access 重命名表，请参考文章：在Access数据库中重命名表)
sp_rename \'表名\', \'新表名\', \'OBJECT\'
新建约束：
ALTER TABLE [表名] ADD CONSTRAINT 约束名 CHECK ([约束字段] <= \'2000-1-1\')
from SC,SCX
where not exists(
select *
from SC SCY
where SCY.Sno=95001 and
not exists(
select *
from SC SCZ
having(avg(grade)>80);
(3)法二
seleCt sno, avg(grade) ' average'
from SC
group by sno
having(avg(grade)>80);
(4)
delete from SC
where SC.sno in(
seleCt sno
新增字段：
ALTER TABLE [表名] ADD [字段名] NVARCHAR (50) NULL
删除字段：
ALTER TABLE [表名] DROP COLUMN [字段名]
修改字段：
ALTER TABLE [表名] ALTER COLUMN [字段名] NVARCHAR (50) NULL
group by SC.sno;
(7)
seleCt S.sname as 姓名 ,grade as 成绩 ,ame as 选修课程
from SC,S,C
where S.sno=SC.sno and o=o and o in(
seleCt cno
from Student,SC
where SC.sno not in(
seleCt SC.sno
from SC
where Cno='C2' )and SC.sno=S.sno;
(3)
seleCt sno, avg(grade) as average
from SC
group by sno
(9)
select Sname
from S
where not exists(
select *
from SC
where Sno=S.Sno and Cno=1);
（10）
select Sname
from S
where not exists(
foreign key(Cno)references course(Cno)
)
(1)
seleCt top 1 S.sno,sname
from SC,S
where Cno='C2' and SC.sno=S.sno
order by grade desC;
(2)
seleCt sname,age
from C
where cname='DB');
(8)
select TOP 1 sno as 学号,grade as 分数,cname as 课程名
from SC,C
where o=o and cname='OS'
order by grade desc;
(
sno char(6),
cno char (8),
constraint PK_SC primary key (sno,cno),
constraint FK_s foreign key (sno) references S(sno),
constraint FK_c foreign key (cno) references C(cno)