Function non_nullable_columns

src/expr/src/relation.rs:2175–2221

Augment non-nullability of columns, by observing either 1. Predicates that explicitly test for null values, and 2. Columns that if null would make a predicate be null.

(predicates: &[MirScalarExpr])

/// 1. Predicates that explicitly test for null values, and
/// 2. Columns that if null would make a predicate be null.
pub fn non_nullable_columns(predicates: &[MirScalarExpr]) -> BTreeSet<usize> {
    let mut nonnull_required_columns = BTreeSet::new();
    for predicate in predicates {
        // Add any columns that being null would force the predicate to be null.
        // Should that happen, the row would be discarded.
        predicate.non_null_requirements(&mut nonnull_required_columns);

        /*
        Test for explicit checks that a column is non-null.

        This analysis is ad hoc, and will miss things:

        materialize=> create table a(x int, y int);
        CREATE TABLE
        materialize=> explain with(types) select x from a where (y=x and y is not null) or x is not null;
        Optimized Plan
        --------------------------------------------------------------------------------------------------------
        Explained Query:                                                                                      +
        Project (#0) // { types: "(integer?)" }                                                             +
        Filter ((#0) IS NOT NULL OR ((#1) IS NOT NULL AND (#0 = #1))) // { types: "(integer?, integer?)" }+
        Get materialize.public.a // { types: "(integer?, integer?)" }                                   +
                                                                                  +
        Source materialize.public.a                                                                           +
        filter=(((#0) IS NOT NULL OR ((#1) IS NOT NULL AND (#0 = #1))))                                     +

        (1 row)
        */

        if let MirScalarExpr::CallUnary {
            func: UnaryFunc::Not(scalar_func::Not),
            expr,
        } = predicate
        {
            if let MirScalarExpr::CallUnary {
                func: UnaryFunc::IsNull(scalar_func::IsNull),
                expr,
            } = &**expr
            {
                if let MirScalarExpr::Column(c, _name) = &**expr {
                    nonnull_required_columns.insert(*c);
                }
            }
        }
    }

    nonnull_required_columns
}

impl CollectionPlan for MirRelationExpr {
    /// Collects the global collections that this MIR expression directly depends on, i.e., that it