sql 判断表是否存在，判断列是否存在

SELECT  * FROM dbo.SysObjects where id = object_id(N‘表名‘)  

SELECT  * FROM dbo.SysObjects where id = object_id(N‘ExchangeLog‘)

if exists(SELECT * FROM dbo.SysObjects where id = object_id(N‘ExchangeLog‘))
　　print ‘表存在‘
else
　　print ‘表不存在‘

select * from syscolumns where id=object_id(N‘表名‘) and name =‘列名‘

select * from syscolumns where id=object_id(N‘ExchangeLog‘) and name =‘Extype‘

if exists(select * from syscolumns where id=object_id(N‘ExchangeLog‘) and name =‘Extype‘)
	alter table ExchangeLog drop column ExType
else
begin
	alter table [ExchangeLog] add ExType nchar(15)
end
go