presto-main/src/main/java/io/prestosql/sql/planner/iterative/rule/ReorderJoins.java/ReorderJoins/isJoinEqualityCondition
class ReorderJoins:        private static boolean isJoinEqualityCondition(Expression expression)
        {
            return expression instanceof ComparisonExpression
                    && ((ComparisonExpression) expression).getOperator() == EQUAL
                    && ((ComparisonExpression) expression).getLeft() instanceof SymbolReference
                    && ((ComparisonExpression) expression).getRight() instanceof SymbolReference;
        }