NOT IN Operator not working as expected in Oracle

Question

I have two tables: PROD and CUST On running the below query in SQL and SYBASE, it works. Oracle is not giving any results.

select * FROM PROD
where PROD.SECID NOT IN (SELECT CUST.SECID FROM CUST WHERE SECID <> '')

NOTE: PROD.SECID has all null values. CUST.SECID has all non null values(valid values).

<>'' doesn't fetch any records from inner subquery so i changed it to IS NOT NULL and now it fetches the results.

但问题是，当查询作为一个整体运行时，它不会给出任何应有的结果。

Answer 1

NOT IN 正常工作。如果你有空值，你不能说它是“在”给定的集合中还是没有。

SQL> select case
  2         when null in (1, 2, 3) then 'in'
  3         when null not in (1, 2, 3) then 'not in'
  4         else 'null'
  5         end as result
  6  from dual;

RESULT
------
null     

如果你想排除给定的值，你应该使用not exists，或者更好的是反连接：

select p.*
from prod p, cust c
where p.secid = c.secid (+)
and c.secid is null;