3.3.1. Columns

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

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General
#	Field	Group box	Description
1	Type	Data type	This attribute handles the data type assigned to the column.
2	Length	Data type	Length, or number of characters or bits, for the types that accept one, like varchar(n) or bit(n). Disabled for the other types.
3	Precision	Data type	Precision, for the types that accept it, like numeric(p, s), or the number of fractional digits of seconds for time and timestamp. Disabled for the other types.
4	Dimension	Data type	Number of dimensions when the type is an array (type[]). 0 means that the type is not an array.
5	Format	Data type	Read-only preview of the data type as it is written in the SQL code, with length, precision, dimension and other modifiers applied.
6	Default value		This field defines the default value for the column in case none is specified in an INSERT command. How it is filled depends on the option selected below: Expression, Sequence, or Identity.
7	Generated	Default value	This option indicates that the column's default value is generated from other columns' values. For example, say we have a column called height_in that represents the height in inches and another generated column called height_cm that represents the height in centimeters. The value of height_cm can be easily computed from height_in by performing a simple conversion like height_in * 2.54.
8	Expression	Default value	Use this option to set up a simple SQL expression as the default value, typed in the field above. When Generated is checked, the expression is used to generate the column's value.
9	Sequence	Default value	This option is used to configure a default value for serial data types based on a sequence object. Once the sequence is selected, it is converted into an expression like nextval('seq'::regclass).
10	Sequence (selector)	Default value	The sequence of the model used as the default value when the option Sequence is selected. Use the buttons beside the field to pick or clear it.
11	Identity	Default value	This option is used to configure an identity column (introduced in PostgreSQL 10). In recent versions of PostgreSQL, it's also possible to tweak the sequence parameters associated with the identity column.
12	Identity type	Default value	The kind of identity column when the option Identity is selected: ALWAYS or BY DEFAULT.
13	NOT NULL	Default value	Creates a NOT NULL constraint in the column.

References

Generated columns
https://www.postgresql.org/docs/current/ddl-generated-columns.html