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。\
高手给予指教
------解决方案--------------------
-- 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;
------解决方案--------------------
如果你只有一条，还勉强可以保证
select max(dummy) dmy,'hello world' hi from dual where 1=1;
select max(dummy) dmy,'hello world' hi from dual where 1=2;