Oracle使用NVL替换空检查空行

Question

I am running a query to retrieve an integer but want to put a check for nulls. If null I want the query to return 0. How can I do that? I tried this below but it's not working

select NVL(A_COUNT, 0) from MYTABLE where VEH_YEAR = '2003';

If A_COUNT is null I want the query to return 0. In the above case I don't have a value 2003 in VEH_YEAR column. The query works if I have a value 2003 in VEH_YEAR column but A_COUNT is null.

Answer 1

最好的版本是在使用NVL之前使用MAX类的Aggregate函数。

select NVL(MAX(A_COUNT),0) from MYTABLE where VEH_YEAR = '2003';

Answer 2

SELECT NVL((select A_COUNT from MYTABLE where VEH_YEAR = '2003'), 0) A_COUNT from dual;

这工作了。