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[数据库]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1ALTER 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_USAGEWHERE 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.COLUMNSWHERE 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 sysobjectswhere 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 stuInfoDrop Constraint PK_stuNoGo

    -- 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 stuInfoDrop Constraint UQ_stuIDGo

     

    -- 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_stuAddressGo

    -- 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