SQL实现表名更改，列名更改，约束更改

1. 修改表名

   格式：sp_rename tablename,newtablename

   sp_rename tablename,newtablename

2. 修改字段名

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

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

3. 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 

4. 更改字段

   格式：alter table table_name alter column column_name

   ALTER TABLE student ALTER COLUMN name VARCHAR(200)

5. 删除字段

   格式：alter table table_name drop column column_name

   ALTER TABLE student DROP COLUMN nationality;

6. 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'

7. 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'

8. 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'

9. 删除字段约束

   格式：alter table tablename drop constraint constraintname

   ALTER TABLE student DROP CONSTRAINT PK__student__2F36BC5B772B9A0B

10. 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