Commits on Nov 2, 2022

1. opt: use RelExpr instead of ColumnID for reorderjoins relation map …

   The reorderjoins opttester directive previously maintained a map from
   the first column ID of each base relation to the relation's label in
   the output. This could cause a panic for relations that didn't output
   any columns. This patch changes the map to use the relations themselves
   as keys, which prevents the panic.
   
   Release note: None

   

   DrewKimball committed Nov 2, 2022
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2. opt: don't drop LeftJoin filter during join ordering …

   This patch fixes a bug in the join reordering logic that can lead to
   incorrect results due to a dropped filter and incorrect conversion of
   a left join to an inner join. The bug can occur when the join tree
   contains an inner join with a left join as an input, where the inner
   join has two separate conjuncts in its ON condition that reference
   both inputs of the left join. Additionally, the inner join filters
   must not filter NULL values from the right side of the left join
   (or alternatively null-rejection rules must be disabled).
   
   The incorrect transformation looks something like this:
   ```
   (INNER JOIN xy (LEFT JOIN ab (INNER JOIN uv wz ON v = w) ON b = v) ON a = x AND u = x)
   ```
   =>
   ```
   (INNER JOIN ab (INNER JOIN xy (INNER JOIN uv wz ON v = w) ON u = x) ON a = x)
   ```
   Notice how `xy` has been "pushed" into the right side of the left
   join and the left join's `b = v` filter (and the left join itself)
   dropped in the process.
   
   To understand what causes the bug, it is necessary to understand three
   points about the join reordering algorithm:
   1. Cross products are never introduced in the enumerated plans. So, for
      two sub-plans, a join is only considered between them if there is an
      applicable edge between those sub-plans.
   2. The original paper associates each join with exactly one edge in the
      hypergraph that encodes "reorderability" properties.
   3. The `JoinOrderBuilder` departs from the paper by associating each
      inner join *conjunct* with a hypergraph edge. This allows each
      conjunct to be independently reordered from the others. See the
      `Special handling of inner joins` section in the `JoinOrderBuilder`
      comment for more details.
   
   (1) combined with (2) implies that a reordered join tree is only
   considered if every edge in the hypergraph could be applied to form joins
   in the join tree. This allows the original algorithm to prevent invalid
   orderings by making just a single edge inapplicable. However, because
   of (3) the same is no longer true for the `JoinOrderBuilder`. In the
   example given above, the left join fails the applicability check,
   indicating an invalid plan. However, the inner join's `a = x` filter
   passes the check and ends up replacing the left join. This prevents
   the the check in (1) from catching the invalid plan.
   
   This patch fixes the bug by keeping track of the edges that *should*
   be applied somewhere in each join tree based on the TES of each edge.
   This is then compared against the actual edges that are applied in
   the construction of the join tree. If the edge sets aren't equal,
   the plan is invalid and cannot be added to the memo. This allows the
   `JoinOrderBuilder` to recover the property that an inapplicable edge
   invalidates an enumerated plan.
   
   Fixes #90761
   
   Release note (bug fix): Fixed a bug existing since 20.2 that could
   cause incorrect results in rare cases for queries with inner joins
   and left joins. For the bug to occur, the left join had to be in
   the input of the inner join and the inner join filters had to
   reference both inputs of the left join, and not filter NULL values
   from the right input of the left join. Additionally, the right input
   of the left join had to contain at least one join, with one input not
   referenced by the left join's ON condition.

   

   DrewKimball committed Nov 2, 2022
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