exists & select 1 from

確認資料存在與否

CREATE TABLE TT_CHI
(
NUM NUMBER
);

TT_CHI 內部資料

select 1 from TT_CHI where NUM != 0;

select 1 from TT_CHI where NUM = 0;

參考
https://blog.csdn.net/qiuzhi__ke/article/details/53018024