Building Blocks

Basic Queries

Nested Structures

Advanced EdgeQL

EdgeQL Tutorial

Subtopics

EdgeQL Tutorial

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, "count" will give the number of elements in an empty set:

Input

Run

Output

Press the 'Run' button to evaluate the input

The `EXISTS`

operator returns `false`

if the set is
empty and `true`

otherwise:

Input

Run

Output

Press the 'Run' button to evaluate the input

Usually it is necessary to provide the type of the empty
set using a cast, when the type is relevant and cannot
be assumed (like in `INSERT`

queries):

Input

Run

Output

Press the 'Run' button to evaluate the input

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:

Input

Run

Output

Press the 'Run' button to evaluate the input

Input

Run

Output

Press the 'Run' button to evaluate the input

Input

Run

Output

Press the 'Run' button to evaluate the input

Because of its ability of making any Cartesian product into another empty set, there are some gotchas when an empty set is used where an array or tuple element are expected:

Input

Run

Output

Press the 'Run' button to evaluate the input

Input

Run

Output

Press the 'Run' button to evaluate the input

Typically, if you want to splice 0 or 1 elements into an
array the "array_agg" function and concatenation should
be used. Try the following example with different values
specified for `x`

:

Input

Run

Output

Press the 'Run' button to evaluate the input