SQL查询表中是否存在某个字段

IF exists (select * from syscolumns where name='字段名' and id=object_id('表名'))
begin
　　　　select '已存在，不需添加！'
end
　　ELSE 
begin
　　　　ALTER TABLE dbo.MQ_PhysicalRoomAndExamineRoom add PhysicalRoomHISCode VARCHAR(36) 
        EXEC sys.sp_addextendedproperty @name=N'MS_Description', @value=N'注释' , @level0type=N'SCHEMA',@level0name=N'dbo', @level1type=N'TABLE',@level1name=N'表名', @level2type=N'COLUMN',@level2name=N'字段名'
end