AssHero commented on code in PR #2823:
URL: https://github.com/apache/arrow-datafusion/pull/2823#discussion_r912578893
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datafusion/optimizer/src/eliminate_limit.rs:
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@@ -35,35 +35,80 @@ impl EliminateLimit {
}
}
+fn eliminate_limit(
+ _optimizer: &EliminateLimit,
+ upper_offset: usize,
+ plan: &LogicalPlan,
+ _optimizer_config: &OptimizerConfig,
+) -> Result<LogicalPlan> {
+ match plan {
+ LogicalPlan::Limit(Limit {
+ skip: offset,
+ fetch: limit,
+ input,
+ ..
+ }) => {
+ // If upper's offset is equal or greater than current's limit,
+ // replaces with an [LogicalPlan::EmptyRelation].
+ // For such query: select * from (select * from xxx limit 5) a
limit 2 offset 5;
+ match limit {
+ Some(limit) => {
+ if *limit == 0 || upper_offset >= *limit {
+ return Ok(LogicalPlan::EmptyRelation(EmptyRelation {
+ produce_one_row: false,
+ schema: input.schema().clone(),
+ }));
+ }
+ }
+ None => {}
+ }
+
+ let offset = match offset {
+ Some(offset) => *offset,
+ None => 0,
+ };
+
+ let expr = plan.expressions();
+
+ // apply the optimization to all inputs of the plan
+ let inputs = plan.inputs();
+ let new_inputs = inputs
+ .iter()
+ .map(|plan| eliminate_limit(_optimizer, offset, plan,
_optimizer_config))
+ .collect::<Result<Vec<_>>>()?;
+
+ from_plan(plan, &expr, &new_inputs)
+ }
+ // Rest: recurse and find possible LIMIT 0/Multi LIMIT OFFSET nodes
+ _ => {
+ // For those plans(projection/sort/..) which do not affect the
output rows of sub-plans, we still use upper_offset;
+ // otherwise, use 0 instead.
+ let offset = match plan {
Review Comment:
For join plan, the upper_offset is set to 0, and the limit node for the join
is not affected.
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