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https://issues.apache.org/jira/browse/CALCITE-3508?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16975780#comment-16975780
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Scott Reynolds commented on CALCITE-3508:
-----------------------------------------
Thank you for the subject change it is considerably better! Updated pull
request title to reflect that as well.
Looking at
{code:java}
JoinProjectTransposeRule{code}
I see that it is using
{code:java}
/** Returns whether all expressions in a list are strong. */
public static boolean allStrong(List<RexNode> operands)
{code}
Today, this will return true for
{code:java}
a.name <> 'Victor'{code}
. Is that a what we should expect from
{noformat}public static boolean isStrong(RexNode){noformat}
? Perhaps we should extend that to cover more cases?
{code:java}
/**
* Returns whether a given expression is strong.
*
* <p>Examples:</p>
* <ul>
* <li>Returns true for {@code c = 1} since it returns null if and only if
* c is null
* <li>Returns false for {@code c IS NULL} since it always returns TRUE
* or FALSE
*</ul>
*
* @param e Expression
* @return true if the expression is strong, false otherwise
*/
public static boolean isStrong(RexNode e)
{code}
To handle `RexCall`s with negations etc?
> 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: 0.5h
> 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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