[Impala-ASF-CR] IMPALA-10681: [WIP] Fix join cardinality if one side is scalar

[Zoltan Borok-Nagy (Code Review)]

Zoltan Borok-Nagy has posted comments on this change. ( 
http://gerrit.cloudera.org:8080/17387 )

Change subject: IMPALA-10681: [WIP] Fix join cardinality if one side is scalar
......................................................................


Patch Set 1:

Thanks Aman for working on this.

I've found the following queries where the cardinality for LEFT SEMI JOIN and 
INNER JOIN still differs.

This kind of query is especially important for us:

 explain select * from store_sales
         inner join (select max(s_store_sk) as max_store_sk from store
                     union
                     select min(s_store_sk) as max_store_sk from store) v
         on ss_store_sk = max_store_sk;

In the above query LHS NDV is 6 while RHS cardinality is 2, therefore join 
output cardinality should be LHS CARD / 3, just like LEFT SEMI JOIN calculates.

The planner also calculates wrong cardinalities for this:

 explain select * from store_sales
         inner join (select max(s_store_sk) as max_store_sk
                     from store group by s_market_id limit 3) v
         on ss_store_sk = max_store_sk;


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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: comment
Gerrit-Change-Id: I8aa9d3b8f3c4848b3e9414fe19ad7ad348d12ecc
Gerrit-Change-Number: 17387
Gerrit-PatchSet: 1
Gerrit-Owner: Aman Sinha <amsi...@cloudera.com>
Gerrit-Reviewer: Impala Public Jenkins <impala-public-jenk...@cloudera.com>
Gerrit-Reviewer: Zoltan Borok-Nagy <borokna...@cloudera.com>
Gerrit-Comment-Date: Mon, 03 May 2021 10:37:16 +0000
Gerrit-HasComments: No