added postgresql

wiki/docker/postgres.md

@@ -1,6 +1,6 @@
 # postgres
 
-This is a [Docker](/wiki/docker.md) container for a postgresql database.
+This is a [Docker](/wiki/docker.md) container for a [postgresql database](/wiki/postgresql.md).
 The official container and documentation was made by
 [Postgres](https://hub.docker.com/_/postgres).
 The Docker container is mainly used in combination with other containers.

wiki/postgresql.md

@@ -0,0 +1,59 @@
+# PostgreSQL
+
+[PostgreSQL](https://www.postgresql.org/) is a free and open-source relational database managment
+system. 
+
+## Setup
+
+The software can be setup via [Docker](/wiki/docker.md) with the
+[postgres image](/wiki/docker/postgres.md).
+
+## Usage
+
+This section addresses the usage of PostgreSQL.
+
+### Basic Usage
+
+This section describes the basic usage and is based on a
+[blog entry on Neon](https://neon.com/postgresql/postgresql-administration/postgresql-show-tables).
+
+The following command can be used to connect to the database and is needed to be run first. 
+`<user>` is the username and `<database>` the name of the database set up for the database.
+
+```sh
+psql -U <user> -d <database>
+```
+
+Alternatively the previous command can be run without the `-d` flag and the following command can
+be run afterwards to change the current database.
+
+```sh
+\c <database>
+```
+
+Afterwards the following command can be used to show all tables in the database.
+
+```sh
+\dt
+```
+
+By appending a `+` additional information can be shown
+
+```sh
+\dt+
+```
+
+Similar to this the following command can be used to show details of a specific table `<table>`.
+
+```sh
+\d <table>
+```
+
+Here a `+` can also be appended to gain more information.
+
+```sh
+\d+ <table>
+```
+
+Finally and most importantly classic SQL statements - for example `SELECT`-statements - can be used
+too when being logged in to a database.