Function compare_sort_values 

pub fn compare_sort_values(a: &Value, b: &Value) -> Ordering

Order of two non-NULL values for an ORDER BY over output rows (window ORDER BY, post-aggregate ORDER BY). Text orders by its bytes, so "10" sorts before "9". Booleans sort false first. Any other pair takes compare_values: numbers by their exact reading, NaN above every number. The caller places NULLs.