sql 添加删除字段

SQL代码
use asm
--------删除字段
if exists (select * from syscolumns where id =object_id('tb_log') and name='COLUMN1')
ALTER TABLE [tb_log ] DROP COLUMN [COLUMN1]

if exists (select * from syscolumns where id =object_id('tb_log') and name='COLUMN2')
ALTER TABLE [tb_log ] DROP COLUMN [COLUMN2]

if exists (select * from syscolumns where id =object_id('tb_log') and name='COLUMN3')
ALTER TABLE [tb_log ] DROP COLUMN [COLUMN3]

if exists (select * from syscolumns where id =object_id('tb_log') and name='COLUMN4')
ALTER TABLE [tb_log ] DROP COLUMN [COLUMN4]

---------添加字段
alter table tb_log add COLUMN5 nvarchar(200), COLUMN6 int