* An existing alias is compatible if (a) it is a sibling of `$clause`
* (ie, it's under the scope of the same relation), and (b) the combination
* of operator and relation between the clauses allows for a shared table join.
* An existing alias is compatible if (a) it is a sibling of `$clause`
* (ie, it's under the scope of the same relation), and (b) the combination
* of operator and relation between the clauses allows for a shared table join.