Struct datafusion_optimizer::eliminate_outer_join::EliminateOuterJoin

pub struct EliminateOuterJoin;

Attempt to replace outer joins with inner joins.

Outer joins are typically more expensive to compute at runtime than inner joins and prevent various forms of predicate pushdown and other optimizations, so removing them if possible is beneficial.

Inner joins filter out rows that do match. Outer joins pass rows that do not match padded with nulls. If there is a filter in the query that would filter any such null rows after the join the rows introduced by the outer join are filtered.

For example, in the select ... from a left join b on ... where b.xx = 100;

For rows when b.xx is null (as it would be after an outer join), the b.xx = 100 predicate filters them out and there is no need to produce null rows for output.

Generally, an outer join can be rewritten to inner join if the filters from the WHERE clause return false while any inputs are null and columns of those quals are come from nullable side of outer join.

Implementations

impl EliminateOuterJoin

pub fn new() -> Self

Trait Implementations

impl Default for EliminateOuterJoin

fn default() -> EliminateOuterJoin

Returns the “default value” for a type.

impl OptimizerRule for EliminateOuterJoin

Attempt to eliminate outer joins.

fn try_optimize( &self, plan: &LogicalPlan, _config: &dyn OptimizerConfig ) -> Result<Option<LogicalPlan>>

Try and rewrite plan to an optimized form, returning None if the plan cannot be optimized by this rule.

fn name(&self) -> &str

A human readable name for this optimizer rule

fn apply_order(&self) -> Option<ApplyOrder>

How should the rule be applied by the optimizer? See comments on ApplyOrder for details.