[jira] [Created] (IMPALA-10322) Constant folding in the SelectList using predicates

["Quanlong Huang (Jira)" <ji...@apache.org>]

Quanlong Huang created IMPALA-10322:
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             Summary: Constant folding in the SelectList using predicates
                 Key: IMPALA-10322
                 URL: https://issues.apache.org/jira/browse/IMPALA-10322
             Project: IMPALA
          Issue Type: Improvement
          Components: Frontend
            Reporter: Quanlong Huang


It seems like we are missing some opportunities for constant folding in the select list using the predicates. In the following query:
{code:sql}
select count(if(year=2010, 1, null)) from functional.alltypes
  where year=2010;
{code}
The plan is 
{code:java}
| PLAN-ROOT SINK                                              |
| |                                                           |
| 03:AGGREGATE [FINALIZE]                                     |
| |  output: count:merge(if(`year` = 2010, 1, NULL))          |
| |  row-size=8B cardinality=1                                |
| |                                                           |
| 02:EXCHANGE [UNPARTITIONED]                                 |
| |                                                           |
| 01:AGGREGATE                                                |
| |  output: count(if(`year` = 2010, 1, NULL))                |
| |  row-size=8B cardinality=1                                |
| |                                                           |
| 00:SCAN HDFS [functional.alltypes]                          |
|    partition predicates: `year` = 2010                      |
|    HDFS partitions=12/24 files=12 size=239.77KB             |
|    row-size=4B cardinality=3.65K
{code}
"if(year=2010, 1, null)" can be rewritten to "1" since the year column will always be 2010. So it can be rewritten to
{code:sql}
select count(1) from functional.alltypes
  where year=2010;
{code}
This save the evalution of the IF function which is usually slow.



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