datafusion-optimizer 20.0.0

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//   http://www.apache.org/licenses/LICENSE-2.0
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use crate::optimizer::ApplyOrder;
use crate::{OptimizerConfig, OptimizerRule};
use datafusion_common::Result;
use datafusion_expr::utils::expand_wildcard;
use datafusion_expr::Distinct;
use datafusion_expr::{Aggregate, LogicalPlan};
use ApplyOrder::BottomUp;

/// Optimizer that replaces logical [[Distinct]] with a logical [[Aggregate]]
///
/// ```text
/// SELECT DISTINCT a, b FROM tab
/// ```
///
/// Into
/// ```text
/// SELECT a, b FROM tab GROUP BY a, b
/// ```

/// Optimizer that replaces logical [[Distinct]] with a logical [[Aggregate]]
#[derive(Default)]
pub struct ReplaceDistinctWithAggregate {}

impl ReplaceDistinctWithAggregate {
    #[allow(missing_docs)]
    pub fn new() -> Self {
        Self {}
    }
}

impl OptimizerRule for ReplaceDistinctWithAggregate {
    fn try_optimize(
        &self,
        plan: &LogicalPlan,
        _config: &dyn OptimizerConfig,
    ) -> Result<Option<LogicalPlan>> {
        match plan {
            LogicalPlan::Distinct(Distinct { input }) => {
                let group_expr = expand_wildcard(input.schema(), input)?;
                let aggregate = LogicalPlan::Aggregate(Aggregate::try_new_with_schema(
                    input.clone(),
                    group_expr,
                    vec![],
                    input.schema().clone(), // input schema and aggregate schema are the same in this case
                )?);
                Ok(Some(aggregate))
            }
            _ => Ok(None),
        }
    }

    fn name(&self) -> &str {
        "replace_distinct_aggregate"
    }

    fn apply_order(&self) -> Option<ApplyOrder> {
        Some(BottomUp)
    }
}

#[cfg(test)]
mod tests {
    use crate::replace_distinct_aggregate::ReplaceDistinctWithAggregate;
    use crate::test::{assert_optimized_plan_eq, test_table_scan};
    use datafusion_expr::{col, LogicalPlanBuilder};
    use std::sync::Arc;

    #[test]
    fn replace_distinct() -> datafusion_common::Result<()> {
        let table_scan = test_table_scan().unwrap();
        let plan = LogicalPlanBuilder::from(table_scan)
            .project(vec![col("a"), col("b")])?
            .distinct()?
            .build()?;

        let expected = "Aggregate: groupBy=[[test.a, test.b]], aggr=[[]]\
                            \n  Projection: test.a, test.b\
                            \n    TableScan: test";

        assert_optimized_plan_eq(
            Arc::new(ReplaceDistinctWithAggregate::new()),
            &plan,
            expected,
        )
    }
}