[ https://issues.apache.org/jira/browse/CALCITE-3508?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16975520#comment-16975520 ]
Julian Hyde commented on CALCITE-3508: -------------------------------------- I changed the subject, because "FILTER clause" is an ambiguous - some people might think it referred to, say, "SUM(x) FILTER (WHERE y > 0)". > 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. -- This message was sent by Atlassian Jira (v8.3.4#803005)