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content/SQL/Postgress setup.md

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+## Install PostgreSQL 12 on Ubuntu 20.04 LTS
+
+```bash
+sudo apt update
+sudo apt install -y postgresql postgresql-contrib postgresql-client
+sudo systemctl status postgresql.service
+```
+
+## Initial database connection
+
+A local connection (from the database server) can be done by the following command:
+
+```bash
+sudo -u postgres psql
+
+psql (12.12 (Ubuntu 12.12-0ubuntu0.20.04.1))
+Type "help" for help.
+
+postgres=#
+```
+
+## Set password for postgres database user
+
+The password for the `postgres` database user can be set the the quick command `\password`
+or by `alter user postgres password 'Supersecret'`. A connection using the `postgres` user
+is still not possible from the "outside" hence to the default settings in the `pg_hba.conf`.
+
+### Update pg_hba.conf to allow postgres user connections with password
+
+In order to allow connections of the `postgres` database user not using OS user
+authentication, you have to update the `pg_hba.conf` which can be found under
+`/etc/postgresql/12/main/pg_hba.conf`.
+
+```shell
+sudo vi /etc/postgresql/12/main/pg_hba.conf
+
+...
+local   all             postgres                                peer
+...
+```
+
+Change the last section of the above line to `md5`.
+
+```
+local   all             postgres                                md5
+```
+
+A restart is required in order to apply the new configuration:
+
+```bash
+sudo systemctl restart postgresql
+```
+
+Now a connection from outside the database host is possible e.g.
+
+```bash
+psql -U postgres -d postgres -h databasehostname
+```
+
+## Creation of additional database users
+
+A database user can be created by the following command:
+
+```sql
+create user myuser with encrypted password 'Supersecret';
+CREATE ROLE
+
+postgres=# \du
+                                   List of roles
+ Role name |                         Attributes                         | Member of
+-----------+------------------------------------------------------------+-----------
+ myuser    |                                                            | {}
+ postgres  | Superuser, Create role, Create DB, Replication, Bypass RLS | {}
+```
+
+## Creation of additional databases
+
+One can create new Postgres databases within an instance. Therefore you can use the `psql`
+command to login (see above).
+
+```sql
+CREATE DATABASE dbname OWNER myuser;
+CREATE DATABASE
+
+postgres=# \l
+                                  List of databases
+   Name    |  Owner   | Encoding |   Collate   |    Ctype    |   Access privileges
+-----------+----------+----------+-------------+-------------+-----------------------
+ dbname    | myuser   | UTF8     | en_US.UTF-8 | en_US.UTF-8 |
+ postgres  | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |
+ template0 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/postgres          +
+           |          |          |             |             | postgres=CTc/postgres
+ template1 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/postgres          +
+           |          |          |             |             | postgres=CTc/postgres
+```
+
+You can leave the `OWNER` section of the command, when doing so, the current user will become
+owner of the newly created database.
+
+To change the owner of an existing database later, you can use the following command:
+
+```sql
+postgres=# alter database dbname owner to myuser;
+ALTER DATABASE
+```