[jira] [Updated] (CALCITE-3508) Strengthen outer Join to inner if it is under a Filter that discards null values

["Julian Hyde (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CALCITE-3508?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Julian Hyde updated CALCITE-3508:
---------------------------------
    Summary: Strengthen outer Join to inner if it is under a Filter that discards null values  (was: Strengthen Outer Joins based on FILTER clauses)

> Strengthen outer Join to inner if it is under a Filter that discards null values
> --------------------------------------------------------------------------------
>
>                 Key: CALCITE-3508
>                 URL: https://issues.apache.org/jira/browse/CALCITE-3508
>             Project: Calcite
>          Issue Type: Improvement
>            Reporter: Scott Reynolds
>            Priority: Major
>              Labels: pull-request-available
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> Today, FilterJoinRule given an Outer Join the rule strengthens it to Inner Join when the nullable side contains a filter IS_NOT_NULL. Below is the code.
> {code:java}
> for (RexNode filter : aboveFilters) {
>       if (joinType.generatesNullsOnLeft()
>           && Strong.isNotTrue(filter, leftBitmap)) {
>         joinType = joinType.cancelNullsOnLeft();
>       }
>       if (joinType.generatesNullsOnRight()
>           && Strong.isNotTrue(filter, rightBitmap)) {
>         joinType = joinType.cancelNullsOnRight();
>       }
>       if (!joinType.isOuterJoin()) {
>         break;
>       }
>     }
> {code}
> This code looks at the filter to determine if it is always true, then it can alter the join type by removing the null on that side.
> We can see this in the following test RelOptRules#testStrengthenJoinType, which executes the following SQL that transforms from a LEFT OUTER JOIN to an INNER JOIN
> {code:sql}
> select *
> from dept left join emp on dept.deptno = emp.deptno
> where emp.deptno is not null and emp.sal > 100
> {code}
> This ticket is about broadening the application of this rule to a sql like the following:
> {code:sql}
> select *
> from dept left join emp on dept.deptno = emp.deptno
> where emp.sal > 100
> {code}
>  This originally came up on the mailing list: [https://mail-archives.apache.org/mod_mbox/calcite-dev/201909.mbox/browser]
> and in that thread it was pointed out that there are filters that prevent this from being applied:
> {code:sql}
> SELECT b.title
> FROM Book b
> LEFT JOIN Author a ON b.author = a.id
> WHERE a.name <> 'Victor'
> {code}
> This means we need to ensure we that the OUTER JOIN doesn't contain – for lack of a different term – negation filters. If there is a negation – like NOT_EQUAL – the JOIN cannot be strengthened.



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