Basically, it turns into a classical bit that houses only a single value.

This is an index lookup that MySQL knows will return at most a single value.

This means that services can only be assigned to a host in one-to-one single value queries.

In other words, it turns into an ordinary bit capable of holding only a single value.

This means that the script or program that fetches the required information must return a single value.

The function itself must return a single value, whose type is defined in the header of the function.

The results of the conditions are single values rather than a number of actions to be taken.