To create a 1-to-1 relationship between Entity A and Entity B, what must be done?

To establish a 1-to-1 relationship between Entity A and Entity B, the most efficient approach involves ensuring that the identifier of Entity B corresponds directly to the identifier of Entity A. This means that for every record in Entity A, there should be exactly one corresponding record in Entity B, and vice versa. By setting the data type of Entity B's identifier to match Entity A's identifier, you effectively create a direct link between the two entities.

This direct matching of identifiers ensures that each record in Entity B uniquely relates back to a record in Entity A, which is fundamental in defining a 1-to-1 relationship. Without this direct connection, you may inadvertently allow misalignments or create the potential for multiple entries in either entity that could violate the intended one-to-one constraint.

Creating additional entities or composite identifiers, as suggested in other options, would complicate the design and dilute the simplicity of a straightforward 1-to-1 relationship. Therefore, setting Entity B's identifier to match Entity A's identifier is the most effective method to achieve the desired relationship.