SqlServer判断表、列不存在则创建

if not exists (select * from sysobjects where id = object_id(‘mytab‘) 
and OBJECTPROPERTY(id, ‘IsUserTable‘) = 1)
create table  mytab
(
   id int,
   age int ,
   name varchar(max),
   primary key (id,age)
)
go

if not exists (select * from syscolumns where id=object_id(‘mytab‘) and name=‘columnname‘) alter table [mytab] add columnname nvarchar(max)