Question

在数据库teacher_class下，写出创建教师表、课程表、授课表的SQL语句，各表结构如下所示：

1.建表语句2、通过SQL语句修改数据表结构：(1) 为 授课表(tc)添加“修课类别”列，此列的定义为Type NCHAR（1），允许空。(2) 在 授课表(tc)中将新添加的Type列的数据类型修改为 NCHAR（2）。(3) 删除授课表(tc)中的Type列。

Answer 1

（1）alter table tc add ‘修课类别’ nchar（1）；
（2）alter table tc modify ‘修课类别’ nchar（2）;
（3）alter table tc drop column ‘修课类别’；

Answer 2

好的，稍等哈

追答

哦哦

有的

稍等

太多了

怎么给你

CREATE TABLE [dbo].[teachers](
[tno] [char](7) NOT NULL,
[tname] [nchar](5) NOT NULL,
[tsex] [char](2) NOT NULL,
[birthday] [smalldatetime] NULL,
[dept] [char](20) NULL,
[phone] [char](8) NULL,
CONSTRAINT [PK_teachers] PRIMARY KEY CLUSTERED
(
[tno] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

SET ANSI_PADDING OFF
GO

ALTER TABLE [dbo].[teachers] WITH CHECK ADD CONSTRAINT [CK_teachers] CHECK (([tsex]='女' OR [tsex]='男'))
GO

ALTER TABLE [dbo].[teachers] CHECK CONSTRAINT [CK_teachers]
GO

ALTER TABLE [dbo].[teachers] WITH CHECK ADD CONSTRAINT [CK_teachers_1] CHECK (([phone] like '[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]'))
GO

ALTER TABLE [dbo].[teachers] CHECK CONSTRAINT [CK_teachers_1]
GO

CREATE TABLE [dbo].[courses](
[cno] [char](10) NOT NULL,
[cname] [char](20) NOT NULL,
[credit] [tinyint] NOT NULL,
[ctype] [char](10) NOT NULL,
CONSTRAINT [PK_courses] PRIMARY KEY CLUSTERED
(
[cno] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

SET ANSI_PADDING OFF
GO

ALTER TABLE [dbo].[courses] WITH CHECK ADD CONSTRAINT [CK_courses] CHECK (([credit]>(0)))
GO

ALTER TABLE [dbo].[courses] CHECK CONSTRAINT [CK_courses]
GO

ALTER TABLE [dbo].[courses] ADD CONSTRAINT [DF_courses_ctype] DEFAULT ('必修') FOR [ctype]
GO

CREATE TABLE [dbo].[tc

alter table tc add type Nchar(1) default null;
alter table tc modify type nchar(2);
alter table tc drop column type;