So you have an existing database in PostGres that you wish to add the PostGIS extension to.
You will need to be logged in with a username that has superuser privileges.
Here let me do this using the postgres default account that on my instance has superuser access.
Here rather than logging in at the start I am choosing to change the connection to a different database
This is done by using
Please note that the semicolon is vital in performing the instruction.
The way I have discovered to do this is by opening the database and then allocating the postgis extension to the database once it is open.
Let us first examine the tables in our blank database before the extension is enabled.
Now let us enable the extension.
CREATE EXTENSION postgis;
Let us now examine the database tables
Enabling the PostGIS extension adds this table along with the ability to add geometry types of varaibles within tables.