sqlserver,mysql,db2,oracle中判断字段的值不为空

oracle中：

select distinct columnid from db2admin.yc_visitstat where columnid<>' ' and columnid is not null

select * from 表名 where 字段名<>' ' and 字段名 is not null

sqlserver,mysql,db2中：

select * from 表名 where 字段名 <>''