* - fields: (string[]) to include in the `$vars` to `IDatabase->select()`
* - joins: (array) to include in the `$join_conds` to `IDatabase->select()`
* All tables, fields, and joins are aliased, so `+` is safe to use.
+ * @phan-return array{tables:string[],fields:string[],joins:array}
*/
public function getJoin( $key = null ) {
$key = $this->getKey( $key );