PostgreSQL ORDER BY Sort problem

The default sort is the order by field name,

This can be done if the field is not allowed to be empty.

However, when a field is allowed to be null, the way the order by field name causes:

Ascending (ASC):

Starts with the minimum value ascending, and the last polygon is connected to a value that has a null field value.

Descending (DESC):

Will put the null value as the maximum value in front, obviously this is not the sort result we want.

PostgreSQL offers NULLS first | the last keyword of the ORDER by clause can satisfy the need

... ORDER by last_updated NULLS first

SELECT last_updated      0 1 END,          last_updated ASC;

PostgreSQL ORDER BY Sort problem