BinaryArithmeticResolver is invoked by ExpressionResolver in order to resolve BinaryArithmetic nodes. During resolution, calling BinaryArithmeticWithDatetimeResolver and applying type coercion can result in BinaryArithmetic producing some other type of node or a subtree of nodes. In such cases a downwards traversal is necessary, but not going deeper than the original expression's children, since all nodes below that point are guaranteed to be already resolved.

For example, given a query:

SELECT '4 11:11' - INTERVAL '4 22:12' DAY TO MINUTE

BinaryArithmeticResolver is called for the following expression:

Subtract( Literal('4 11:11', StringType), Literal(Interval('4 22:12' DAY TO MINUTE), DayTimeIntervalType(0,2)) )

After calling BinaryArithmeticWithDatetimeResolver and applying type coercion, the expression is transformed into:

Cast( DatetimeSub( TimeAdd( Literal('4 11:11', StringType), UnaryMinus( Literal(Interval('4 22:12' DAY TO MINUTE), DayTimeIntervalType(0,2)) ) ) ) )

A single Subtract node is replaced with a subtree of nodes. In order to resolve this subtree we need to invoke ExpressionResolver recursively on the top-most node's children. The top-most node itself is not resolved recursively in order to avoid recursive calls to BinaryArithmeticResolver and other sub-resolvers. To prevent a case where we resolve the same node twice, we need to mark nodes that will act as a limit for the downwards traversal by applying a ExpressionResolver.SINGLE_PASS_SUBTREE_BOUNDARY tag to them. These children along with all the nodes below them are guaranteed to be resolved at this point. When ExpressionResolver reaches one of the tagged nodes, it returns identity rather than resolving it. Finally, after resolving the subtree, we need to resolve the top-most node itself, which in this case means applying a timezone, if necessary.