一、SQL语句 修改字段默认值的
1。 建约束
alter table tb_name add constraint dd default 'bbbb ' for column_name
2。删除约束
alter table tb_name drop constraint dd
3。重新建约束
alter table tb_name add constraint dd default 'cccc ' for column_name
二、内容替换 replace
update [swf_Content] set [Description] =replace([Description],'200901/14','200901/15')
update [swf_Content_01] set [content] = replace(convert(varchar(4000), [content]),'200901/14','200901/15') --ntext类型字段转换为varchar
三、添加列并设置默认值
ALTER TABLE TBProduct ADD Discount INT NULL CONSTRAINT TBProduct_Discount_Default DEFAULT 0 WITH VALUES
四、查询表结构（一）
1.Select
col.[name] as '字段名',
col.[length]as '长度',
type.[name] as '类型' ,
pro.value as '描述'
From syscolumns as col
Left Join systypes as type on col.xtype = type.xtype
Left Join sysProperties as pro on col.id = pro.id and col.colid = pro.smallid
where col.id = (Select id From Sysobjects Where name = 'trole')
2.select name from syscolumns where id =(select id from sysobjects where name='trole') order by colorder
五、修改字段类型
ALTER TABLE tbBODetail ALTER COLUMN total MONEY NULL
