SELECT SUM 在没有记录时返回一行
我发现一个查询存在一些问题，该查询从表中返回满足特定条件的所有记录的字段总和.当没有记录时，我希望收到未找到记录"，但我收到的是空结果.
I'm finding some problems with a query that returns the sum of a field from a table for all the records that meet certain conditions. I expected to receive a "No records found' when there were no records, but instead I'm receiving a null result.
SQL> SELECT * FROM DUAL WHERE 1=2;
no rows selected
SQL> SELECT SUM(dummy) FROM DUAL WHERE 1=2;
SUM(DUMMY)
----------
SQL>
在这种情况下有什么办法不接收任何记录吗?
Is there any way to not receive any record in that case?
推荐答案
这个怎么样:
select my_sum
from
(SELECT SUM(dummy) as my_sum FROM DUAL WHERE 1=2)
where
my_sum is not null
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