Method apply_demand

src/repr/src/relation.rs:1444–1468

Creates a new [`RelationDesc`] retaining only the columns specified in `demands`.

(&self, demands: &BTreeSet<usize>)

    /// Creates a new [`RelationDesc`] retaining only the columns specified in `demands`.
    pub fn apply_demand(&self, demands: &BTreeSet<usize>) -> RelationDesc {
        let mut new_desc = self.clone();

        // Update ColumnMetadata.
        let mut removed = 0;
        new_desc.metadata.retain(|idx, metadata| {
            let retain = demands.contains(&idx.0);
            if !retain {
                removed += 1;
            } else {
                metadata.typ_idx -= removed;
            }
            retain
        });

        // Update SqlColumnType.
        let mut idx = 0;
        new_desc.typ.column_types.retain(|_| {
            let keep = demands.contains(&idx);
            idx += 1;
            keep
        });

        new_desc
    }
}

#[cfg(any(test, feature = "proptest"))]