常用数据库定义语言DDL
--1.判断表中是否存在某个字段 select * from SysObjects a left join SysColumns b on a.id = b.id where a.name = 'TableName' and b.Name='ColumnName' --2.在表中新增一个字段 alter table TableName add ColumnName varchar(100) default ('') with values --3.在表中删除一个字段 alter table TableName drop column ColumnName --4.修改表中字段类型 alter table TableName alter column ColumnName new_data_type --5.查询某个字段的默认值 select b.name from syscolumns a,sysobjects b where a.id=object_id('TableName') and b.id=a.cdefault and a.name='IsCanceled' and b.xtype='D' if @defaultName is not null --6.删除默认值 alter table TableName drop constraint DefaultName