Oracle：使用 where 子句选择重复项？

Question

我有一个问题：为什么我不能只使用以下 SQL 查询从PERSON表中获取唯一电子邮件地址的列表？

SELECT NOT DISTINCT Email FROM PERSON

Answer 1

I think the easiest and common way to achieve this is with grouping by the Email column and then keep the records having count = 1.

SELECT Email, COUNT(Email)
FROM PERSON
GROUP BY Email
HAVING COUNT(Email) > 1;

NOT DISTINCT is not working because it is not a valid expression. DISTINCT is used to return only different values, so NOT before it is not working as you expect.

Answer 2

You asked to get a list of unique eMail addresses , which is done by:

SELECT DISTINCT(Email) FROM PERSON;

Standard SQL does not have NOT DISTINCT or anything like that.