3.3.1. Columns

Columns are the small unity of a table and they define how data must be stored through their data types and additional attributes as shown in the image below.

Attribute	Description
Data Type	This attribute handles the data type assigned to the column.
Default Value	This field defines the default value for the column in case of none is specified in a INSERT command. If user want to set up a simple expression use the attribute Expression. The attribute Sequence is used to configure a default value for serial data types based upon a sequence object. Once selected the sequence this object will be converted into an expression like: nextval('seq'::regclass). The Identity attribute is used to configure an identity column (introduced in PostgreSQL 10). The possible values of this field are ALWAYS and BY DEFAULT.
NOT NULL	Creates a NOT NULL constraint in the column.