What must you define to use a hashed internal table efficiently?

To use a hashed internal table efficiently, it is essential to ensure that the key used for the table is fully qualified. When the key is fully qualified, it allows for quick access to table entries because the hashed internal table uses a hashing algorithm to compute the address at which the data is stored. This mechanism drastically reduces the time complexity for both read and write operations compared to other internal table types.

A fully qualified key ensures that there are no ambiguities or collisions in identifying unique entries. In a hashed internal table, every entry must be uniquely identifiable by its key, and if the key is not fully qualified, it can lead to inefficient lookups or even runtime errors if duplicate keys are inadvertently used.

In contrast, while the uniqueness of the key and the data types of the table entries are critical attributes, they do not specifically pertain to the efficiency of its use in relation to hashing. Specifying the maximum size of the table may be useful in some contexts, but it does not directly impact the operational efficiency tied to hashing mechanisms. Therefore, defining a fully qualified key is the most critical requirement for efficiently leveraging hashed internal tables in SAP ABAP programming.