Function scoped_rel_sql 

pub fn scoped_rel_sql(rel: &str, cols: &[String]) -> String

Relation rel (already quoted) restricted to the rows whose cols, as text, are one of the tuples passed as $1::text[], $2::text[], … (one array per column, row-aligned): a subquery to read a binding through (select_bound_sql‘s rel) so an aggregated binding loads only the touched coordinates’ groups.