Sets

There is no NULL value in EdgeDB unlike in many other databases or programming languages. This is deliberate, as NULL scalars create all sorts of problems when interacting with other data and operations.

Instead of the NULL scalar value EdgeDB uses an empty set {} to denote the absence of data. The advantage of using the empty set is that it works exactly like every other set in every way. Its behavior is well-defined and consistent across all operators and functions.

For example, the count function, which returns the number of elements in a set, works just as well with an empty set:

The exists operator returns false if the set is empty and true otherwise:

Usually it is necessary to provide the type of the empty set using a cast, when the type is relevant and cannot be assumed:

In the example above, there is no context to indicate the intended type of this empty set. EdgeQL will not accept the input unless the empty set is given a cast like <int32> or <int64>:

When an empty set is used as an element-wise operand or element-wise parameter of a function, the result is always an empty set too (albeit of whatever the return type is). This is because the Cartesian product of the empty set with anything else is still an empty set:

Because the Cartesian product of anything with an empty set is another empty set, there are some gotchas when an empty set is used where an array or tuple element are expected:

For more on Cartesian multiplication, see Chapter 11 of the Easy EdgeDB book or the Wikipedia page on Cartesian products.

Typically, if you want to splice 0 or 1 elements into an array the array_agg function and concatenation should be used. A look at the function signature shows that it will return an array, which does not have the gotcha mentioned above with an empty set:

std::array_agg(s: set of anytype) -> array<anytype>

Try the following example with different values specified for x: