oracle怎么能给所有select字段赋默认值
类似这样sql：select 字段1，字段2，‘hello，world’ from table1 where 字段1=？，
如果没有数据，还希望输出hello,world，其他两个字段，随便填个值，比如0
必须有where，实际根据这个where条件表里有时会有数据，有时是没有匹配的数据的，但是没有匹配数据的时候还希望输出hello,world，其他两个字段，随便填个值，比如0。\
-- 用union all加以解决： -- 例如： select c1, c2 from (select c1, c2 from tb_name union all select 'hello' as c1, 'world' as c2 from dual) t where rownum=1; select c1, c2 from (select ename as c1, job as c2 from emp where empno=7900 union all select 'hello' as c1, 'world' as c2 from dual) t where rownum=1; select c1, c2 from (select ename as c1, job as c2 from emp where empno=7901 union all select 'hello' as c1, 'world' as c2 from dual) t where rownum=1;
select max(dummy) dmy,'hello world' hi from dual where 1=1; select max(dummy) dmy,'hello world' hi from dual where 1=2;