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enable_implied_pushdown (boolean) ​

  • Default value (as of this release): off

This configuration parameter enables transitive pushdown of qualifiers. When the planner can determine that two columns must be the same value, it will attempt to apply any qualifiers specified for one column to the other column. It then pushes any new qualifiers as far down in the query plan as possible.

In the example below, we can see that A.x and B.y must have the same value. This allows the qualifier y > 3 to be applied to the output of the join. Furthermore, because this is an INNER JOIN, the qualifier can be pushed down to the scan, resulting in even better performance. This effectively adds the clause B.y > 3 to the query during execution.

sql
CREATE TABLE A (x int);
CREATE TABLE B (y int);

SET enable_implied_pushdown TO true;

EXPLAIN SELECT * FROM A INNER JOIN B ON A.x = B.y WHERE A.x > 3;

                                                    QUERY PLAN                                                     
-------------------------------------------------------------------------------------------------------------------
 id   rows_planned   workers   node   
 13              1       all   SELECT   
  1              1       all   INNER HASH JOIN ON (b.y = a.x)   
  4              1       all   |-SCAN a   
                               |   (a.x > $0) AND a.x = bloom(7) AND scan_constraints: min_max(a.x) AND (a.x > $0)
  7              1       all   |-BUILD   
 10              1       all     SCAN b   
                                   (b.y > $2) AND scan_constraints: (b.y > $2)  <-- filter applied to A.x is pushed down to B.y as well