[DRILL-4539] Add support for Null Equality Joins

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Assignee: Roman Kulyk
• Reporter: Jacques Nadeau
• Created: 24/Mar/16 22:04
• Updated: 30/Sep/16 15:27

Description

Tableau frequently generates queries similar to this:

SELECT `t0`.`city` AS `city`,
  `t2`.`X_measure__B` AS `max_Calculation_DFIDBHHAIIECCJFDAG_ok`,
  `t0`.`state` AS `state`,
  `t0`.`sum_stars_ok` AS `sum_stars_ok`
FROM (
  SELECT `business`.`city` AS `city`,
    `business`.`state` AS `state`,
    SUM(`business`.`stars`) AS `sum_stars_ok`
  FROM `mongo.academic`.`business` `business`
  GROUP BY `business`.`city`,
    `business`.`state`
) `t0`
  INNER JOIN (
  SELECT MAX(`t1`.`X_measure__A`) AS `X_measure__B`,
    `t1`.`city` AS `city`,
    `t1`.`state` AS `state`
  FROM (
    SELECT `business`.`city` AS `city`,
      `business`.`state` AS `state`,
      `business`.`business_id` AS `business_id`,
      SUM(`business`.`stars`) AS `X_measure__A`
    FROM `mongo.academic`.`business` `business`
    GROUP BY `business`.`city`,
      `business`.`state`,
      `business`.`business_id`
  ) `t1`
  GROUP BY `t1`.`city`,
    `t1`.`state`
) `t2` ON (((`t0`.`city` = `t2`.`city`) OR ((`t0`.`city` IS NULL) AND (`t2`.`city` IS NULL))) AND ((`t0`.`state` = `t2`.`state`) OR ((`t0`.`state` IS NULL) AND (`t2`.`state` IS NULL))))

If you look at the join condition, you'll note that the join condition is an equality condition which also allows null=null. We should add a planning rewrite rule and execution join option to allow null equality so that we don't treat this as a cartesian join.

Issue Links

• Dependent: CALCITE-1200 Handle null equality join condition as IS NOT DISTINCT FROM in RelOptUtil.splitJoinCondition
• links to: GitHub Pull Request #462