如果select返回null，则选择不同的select

Question

我们需要这样做：

select * 
from table1 as t
where t.num = 111
orderby t.createon

如果没有返回的记录 - 做不同的选择：

select * 
from table1 as t
orderby t.createon

有什么方法可以加入这些选择吗？ 谢谢！

Answer 1

SELECT
    *
FROM
    table1 as t
WHERE
    EXISTS((SELECT * FROM table1 WHERE num = 111) AND t.num = 111)
        OR NOT EXISTS (SELECT * FROM table1 where num = 111)
ORDER BY
    t.createon