datafusion-optimizer 19.0.0

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// to you under the Apache License, Version 2.0 (the
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//
//   http://www.apache.org/licenses/LICENSE-2.0
//
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// software distributed under the License is distributed on an
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// specific language governing permissions and limitations
// under the License.

use crate::optimizer::ApplyOrder;
use datafusion_common::Result;
use datafusion_expr::{Expr, LogicalPlan, Projection};
use std::collections::HashMap;

use crate::push_down_filter::replace_cols_by_name;
use crate::{OptimizerConfig, OptimizerRule};

/// Optimization rule that merge [LogicalPlan::Projection].
#[derive(Default)]
pub struct MergeProjection;

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

impl OptimizerRule for MergeProjection {
    fn try_optimize(
        &self,
        plan: &LogicalPlan,
        _config: &dyn OptimizerConfig,
    ) -> Result<Option<LogicalPlan>> {
        match plan {
            LogicalPlan::Projection(parent_projection) => {
                match parent_projection.input.as_ref() {
                    LogicalPlan::Projection(child_projection) => {
                        let replace_map = collect_projection_expr(child_projection);
                        let new_exprs = parent_projection
                            .expr
                            .iter()
                            .map(|expr| replace_cols_by_name(expr.clone(), &replace_map))
                            .enumerate()
                            .map(|(i, e)| match e {
                                Ok(e) => {
                                    let parent_expr = parent_projection.schema.fields()
                                        [i]
                                        .qualified_name();
                                    if e.display_name()? == parent_expr {
                                        Ok(e)
                                    } else {
                                        Ok(e.alias(parent_expr))
                                    }
                                }
                                Err(e) => Err(e),
                            })
                            .collect::<Result<Vec<_>>>()?;
                        let new_plan =
                            LogicalPlan::Projection(Projection::try_new_with_schema(
                                new_exprs,
                                child_projection.input.clone(),
                                parent_projection.schema.clone(),
                            )?);
                        Ok(Some(
                            self.try_optimize(&new_plan, _config)?.unwrap_or(new_plan),
                        ))
                    }
                    _ => Ok(None),
                }
            }
            _ => Ok(None),
        }
    }

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

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

pub fn collect_projection_expr(projection: &Projection) -> HashMap<String, Expr> {
    projection
        .schema
        .fields()
        .iter()
        .enumerate()
        .flat_map(|(i, field)| {
            // strip alias
            let expr = projection.expr[i].clone().unalias();
            // Convert both qualified and unqualified fields
            [
                (field.name().clone(), expr.clone()),
                (field.qualified_name(), expr),
            ]
        })
        .collect::<HashMap<_, _>>()
}

#[cfg(test)]
mod tests {
    use crate::merge_projection::MergeProjection;
    use datafusion_common::Result;
    use datafusion_expr::{
        binary_expr, col, lit, logical_plan::builder::LogicalPlanBuilder, LogicalPlan,
        Operator,
    };
    use std::sync::Arc;

    use crate::test::*;

    fn assert_optimized_plan_equal(plan: &LogicalPlan, expected: &str) -> Result<()> {
        assert_optimized_plan_eq(Arc::new(MergeProjection::new()), plan, expected)
    }

    #[test]
    fn merge_two_projection() -> Result<()> {
        let table_scan = test_table_scan()?;
        let plan = LogicalPlanBuilder::from(table_scan)
            .project(vec![col("a")])?
            .project(vec![binary_expr(lit(1), Operator::Plus, col("a"))])?
            .build()?;

        let expected = "Projection: Int32(1) + test.a\
        \n  TableScan: test";
        assert_optimized_plan_equal(&plan, expected)
    }

    #[test]
    fn merge_three_projection() -> Result<()> {
        let table_scan = test_table_scan()?;
        let plan = LogicalPlanBuilder::from(table_scan)
            .project(vec![col("a"), col("b")])?
            .project(vec![col("a")])?
            .project(vec![binary_expr(lit(1), Operator::Plus, col("a"))])?
            .build()?;

        let expected = "Projection: Int32(1) + test.a\
        \n  TableScan: test";
        assert_optimized_plan_equal(&plan, expected)
    }

    #[test]
    fn merge_alias() -> Result<()> {
        let table_scan = test_table_scan()?;
        let plan = LogicalPlanBuilder::from(table_scan)
            .project(vec![col("a")])?
            .project(vec![col("a").alias("alias")])?
            .build()?;

        let expected = "Projection: test.a AS alias\
        \n  TableScan: test";
        assert_optimized_plan_equal(&plan, expected)
    }
}