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        为什么 SUM(null) 在 Oracle 中不为 0?

        时间:2023-11-28
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                  本文介绍了为什么 SUM(null) 在 Oracle 中不为 0?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着跟版网的小编来一起学习吧!

                  问题描述

                  遇到空值时,请解释 SUM 函数在 Oracle 中的内部功能,我们将不胜感激:

                  It would be appreciated explaining the internal functionality of SUM function in Oracle, when encountering null values:
                  The result of

                  select sum(null) from dual;
                  is null
                  

                  但是当一个空值在一个值序列中时(比如一个可为空的列的总和),空值的计算值为0

                  But when a null value is in a sequence of values (like sum of a null-able column), the calculated value of null value will be 0

                  select sum(value) from
                  (
                  select case when mod(level , 2) = 0 then null else level end as value from dual
                  connect by level <= 10
                  )
                  is 25
                  

                  看到

                  select (1 + null) from dual
                  is null
                  

                  因为任何带有 null 的操作都会导致 null(除了 is null 运算符).

                  ==========================
                  由于评论而有所更新:

                  As any operation with null will result null (except is null operator).

                  ==========================
                  Some update due to comments:

                  create table odd_table as select sum(null) as some_name from dual;
                  

                  将导致:

                  create table ODD_TABLE
                  (
                    some_name NUMBER
                  )
                  

                  为什么 some_name 列是 number 类型?

                  Why some_name column is of type number?

                  推荐答案

                  SQL 在计算 SUM 时不会将 NULL 值视为零,它会忽略它们:

                  SQL does not treat NULL values as zeros when calculating SUM, it ignores them:

                  返回表达式中所有值的总和,或仅返回 DISTINCT 值.空值被忽略.

                  Returns the sum of all the values, or only the DISTINCT values, in the expression. Null values are ignored.

                  这仅在一种情况下有所不同 - 当被累加的序列不包含数字项时,只有 NULLs:如果至少存在一个数字,则结果将是数字.

                  This makes a difference only in one case - when the sequence being totalled up does not contain numeric items, only NULLs: if at least one number is present, the result is going to be numeric.

                  这篇关于为什么 SUM(null) 在 Oracle 中不为 0?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持跟版网!

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