SQL实现表名更改，列名更改，约束更改

2024-01-03 10:00:16

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

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'

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