SQL实现表名更改，列名更改，约束更改

修改表名

格式：sp_rename tablename,newtablename

sp_rename tablename,newtablename

修改字段名

格式：sp_rename 'tablename.colname',newcolname,'column'

sp_rename 'tablename.colname',newcolname,'column'

添加字段

格式：alter table table_name add new_column data_type [interality_codition]

示例1
ALTER TABLE student Add nationality varchar(20)

--示例2 添加int类型的列,默认值为 0
alter table student add studentName int default 0

   
--示例3 添加int类型的列,默认值为0，主键
alter table student add studentId int primary key default 0    
   
--示例4 判断student中是否存在name字段且删除字段
if exists(select * from syscolumns where id=object_id('student') and name='name') begin   
alter table student DROP COLUMN name    
end 

更改字段

格式：alter table table_name alter column column_name

ALTER TABLE student ALTER COLUMN name VARCHAR(200)

删除字段

格式：alter table table_name drop column column_name

ALTER TABLE student DROP COLUMN nationality;

查看字段约束

格式： select * from information_schema.constraint_column_usage where TABLE_NAME = table_name

SELECT TABLE_NAME,COLUMN_NAME,CONSTRAINT_NAME FROM information_schema.CONSTRAINT_COLUMN_USAGE
WHERE TABLE_NAME = 'student'

查看字段缺省约束表达式 （即默认值等）

格式：select * from information_schema.columns where TABLE_NAME = table_name

SELECT TABLE_NAME, COLUMN_NAME, COLUMN_DEFAULT FROM information_schema.COLUMNS
WHERE TABLE_NAME='student'

查看字段缺省约束名

格式：select name from sysobjects where object_id(table_name)=parent_obj and xtype=’D’

select name from sysobjects
where object_id('表?名?')=parent_obj and xtype='D'

删除字段约束

格式：alter table tablename drop constraint constraintname

ALTER TABLE student DROP CONSTRAINT PK__student__2F36BC5B772B9A0B

添加字段约束

格式：alter table tablename add constraint constraintname primary key (column_name)

--示例1
ALTER TABLE stuInfo ADD CONSTRAINT PK_stuNo PRIMARY KEY (stuNo)

--示例2  添加主键约束（Primary Key）
-- 存在主键约束PK_stuNO，则删除
IF EXISTS(SELECT * FROM sysobjects WHERE name='PK_stuNo' and xtype='PK')
    Alter TABLE stuInfo
Drop Constraint PK_stuNo
Go
-- 重新添加主键约束PK_stuNO
ALTER TABLE stuInfo  ADD CONSTRAINT PK_stuNo PRIMARY KEY (stuNo)
Go

--示例3 添加 唯一UQ约束（Unique Constraint）
-- 存在唯一约束UQ_stuNO，则删除
IF EXISTS(SELECT * FROM sysobjects WHERE name='UQ_stuID' and xtype='UQ')
    Alter TABLE stuInfo
Drop Constraint UQ_stuID
Go
-- 重新添加唯一约束UQ_stuID
ALTER TABLE stuInfo ADD CONSTRAINT UQ_stuID UNIQUE (stuID)

--示例4 添加默认DF约束（Default Constraint）
-- 存在默认约束UQ_stuNO，则删除
IF EXISTS(SELECT * FROM sysobjects WHERE name='DF_stuAddress' and xtype='D')
    Alter TABLE stuInfo Drop Constraint DF_stuAddress
Go
-- 重新添加默认约束DF_stuAddress
ALTER TABLE stuInfo  ADD CONSTRAINT DF_stuAddress DEFAULT ('地址不详') FOR stuAddress

--示例5 检查CK约束（Check Constraint）
-- 存在检查约束UQ_stuNO，则删除
IF EXISTS(SELECT * FROM sysobjects WHERE name='CK_stuAge' and xtype='C')
    Alter TABLE stuInfo Drop Cons

分类: Database-Database