Function mentat_query_projector::projected_column_for_var

pub fn projected_column_for_var(
    var: &Variable, 
    cc: &ConjoiningClauses
) -> Result<(ProjectedColumn, ValueTypeSet)>

Return the projected column -- that is, a value or SQL column and an associated name -- for a given variable. Also return the type. Callers are expected to determine whether to project a type tag as an additional SQL column.