[jira] [Created] (FLINK-3141) Design of NULL values handling in operation

["Chengxiang Li (JIRA)" <ji...@apache.org>]

Chengxiang Li created FLINK-3141:
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             Summary: Design of NULL values handling in operation
                 Key: FLINK-3141
                 URL: https://issues.apache.org/jira/browse/FLINK-3141
             Project: Flink
          Issue Type: Sub-task
            Reporter: Chengxiang Li


We discuss and finalize how NULL value is handled in specified cases here. this is the first proposal:
# NULL compare. In ascending order, NULL is smaller than any other value, and NULL == NULL return false. 
# NULL exists in GroupBy Key, all NULL values are grouped as a single group.
# NULL exists in Aggregate columns, ignore NULL in aggregation function.
# NULL exists in both side Join key, refer to #i, NULL == NULL return false, no output for NULL Join key.
# NULL in Scalar expression, expression within NULL(eg. 1 + NULL) return NULL. 
# NULL in Boolean expression, add an extra result: UNKNOWN, more semantic for Boolean expression in reference #1.




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