Function expr_api

datafusion-examples/examples/query_planning/expr_api.rs:60–98

This example demonstrates the DataFusion [`Expr`] API. DataFusion comes with a powerful and extensive system for representing and manipulating expressions such as `A + 5` and `X IN ('foo', 'bar', 'baz')`. In addition to building and manipulating [`Expr`]s, DataFusion also comes with APIs for evaluation, simplification, and analysis. The code in this example shows how to: 1. Create [`Expr`]s usi

()

/// 6. Get the types of the expressions: [`expression_type_demo`]
/// 7. Apply type coercion to expressions: [`type_coercion_demo`]
pub async fn expr_api() -> Result<()> {
    // The easiest way to do create expressions is to use the
    // "fluent"-style API:
    let expr = col("a") + lit(5);

    // The same same expression can be created directly, with much more code:
    let expr2 = Expr::BinaryExpr(BinaryExpr::new(
        Box::new(col("a")),
        Operator::Plus,
        Box::new(Expr::Literal(ScalarValue::Int32(Some(5)), None)),
    ));
    assert_eq!(expr, expr2);

    // See how to build aggregate functions with the expr_fn API
    expr_fn_demo()?;

    // See how to evaluate expressions
    evaluate_demo()?;

    // See how to simplify expressions
    simplify_demo()?;

    // See how to analyze ranges in expressions
    range_analysis_demo()?;

    // See how to analyze boundaries in different kinds of expressions.
    boundary_analysis_and_selectivity_demo()?;

    // See how boundary analysis works for `AND` & `OR` conjunctions.
    boundary_analysis_in_conjunctions_demo()?;

    // See how to determine the data types of expressions
    expression_type_demo()?;

    // See how to type coerce expressions.
    type_coercion_demo()?;

    Ok(())
}

/// DataFusion's `expr_fn` API makes it easy to create [`Expr`]s for the
/// full range of expression types such as aggregates and window functions.