[GitHub] [incubator-doris] wutiangan opened a new issue #1696: multi sum distianct need return null, not zero

[GitBox <gi...@apache.org>]

wutiangan opened a new issue #1696: multi sum distianct need return null, not zero
URL: https://github.com/apache/incubator-doris/issues/1696
 
 
   mysql> select sum(distinct id), sum(distinct int_col) from alltypesagg;        
   +--------------------+-------------------------+
   | sum(DISTINCT `id`) | sum(DISTINCT `int_col`) |
   +--------------------+-------------------------+
   |                  0 |                       0 |
   +--------------------+-------------------------+
   1 row in set (0.01 sec)
   
   mysql> select sum(distinct id)  from alltypesagg;                       
   +--------------------+
   | sum(DISTINCT `id`) |
   +--------------------+
   |               NULL |
   +--------------------+
   1 row in set (0.01 sec)
   
   当表中没有数据时，sum distinct应该返回NULL， 而不是0，因为0对sum聚合函数来说是有意义的数。单个sum distinct计算结果没有问题，但是多个sum distinct的计算结果有问题。

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