Final answer:
In dynamic programming, the best choice is to consider all possible combinations when evaluating all possible join orders allowing all trees. However, when allowing only left-deep trees, the best choice is to consider join orders that form a b. left-deep tree structure, as this typically improves performance.
Step-by-step explanation:
In dynamic programming, the table entries represent the optimal substructure of the problem being solved. When evaluating all possible join orders allowing all trees, the best choice is to consider all possible combinations and select the one that yields the highest overall value. However, when allowing only left-deep trees, the best choice is to consider join orders that form a left-deep tree structure, as this typically improves performance.