Function evaluate 

pub fn evaluate(
    plan: &Plan,
    expr: ExprRef,
    schema: &Schema,
    chunk: &Chunk,
) -> Result<Vector>

Evaluates one expression over a chunk, producing one vector as long as the chunk.

schema describes chunk, and it is what a column reference resolves against.

Errors

If a column reference names a binding the schema does not have, if an aggregate appears outside an aggregate operator, or anything a kernel reports.