MSSQL-DDL

常用数据库定义语言DDL

--1.判断表中是否存在某个字段

select * from 

SysObjects a left join SysColumns b on a.id = b.id 

where a.name = 'TableName' and b.Name='ColumnName'



--2.在表中新增一个字段

alter table TableName add ColumnName varchar(100) default ('') with values



--3.在表中删除一个字段

alter table TableName drop column ColumnName



--4.修改表中字段类型

alter table TableName alter column ColumnName new_data_type



--5.查询某个字段的默认值

select b.name from syscolumns a,sysobjects b where a.id=object_id('TableName') 

and b.id=a.cdefault and a.name='IsCanceled' and b.xtype='D'

if @defaultName is not null



--6.删除默认值

alter table TableName drop constraint DefaultName