In order to install PostgreSQL on OSX, you need to know which versions are currently supported.

Use this command to see what versions you have available.

sudo port list | grep "^postgresql[[:digit:]]\\{2\\}[[:space:]]"

You should get a list that looks something like the following:

postgresql80                   @8.0.26         databases/postgresql80
postgresql81                   @8.1.23         databases/postgresql81
postgresql82                   @8.2.23         databases/postgresql82
postgresql83                   @8.3.23         databases/postgresql83
postgresql84                   @8.4.22         databases/postgresql84
postgresql90                   @9.0.23         databases/postgresql90
postgresql91                   @9.1.22         databases/postgresql91
postgresql92                   @9.2.17         databases/postgresql92
postgresql93                   @9.3.13         databases/postgresql93
postgresql94                   @9.4.8          databases/postgresql94
postgresql95                   @9.5.3          databases/postgresql95
postgresql96                   @9.6beta2       databases/postgresql96

In this example, the most recent version of PostgreSQL that is supported in 9.6, so we will install that.

sudo port install postgresql96-server postgresql96

You will see an installation log like this:

--->  Computing dependencies for postgresql96-server
--->  Dependencies to be installed: postgresql96
--->  Fetching archive for postgresql96
--->  Attempting to fetch postgresql96-9.6beta2_0.darwin_15.x86_64.tbz2 from         <https://packages.macports.org/postgresql96>
--->  Attempting to fetch postgresql96-9.6beta2_0.darwin_15.x86_64.tbz2.rmd160 from <https://packages.macports.org/postgresql96>
--->  Installing postgresql96 @9.6beta2_0
--->  Activating postgresql96 @9.6beta2_0

To use the postgresql server, install the postgresql96-server port

--->  Cleaning postgresql96
--->  Fetching archive for postgresql96-server
--->  Attempting to fetch postgresql96-server-9.6beta2_0.darwin_15.x86_64.tbz2 from <https://packages.macports.org/postgresql96-server>
--->  Attempting to fetch postgresql96-server-9.6beta2_0.darwin_15.x86_64.tbz2.rmd160 from <https://packages.macports.org/postgresql96-server>
--->  Installing postgresql96-server @9.6beta2_0
--->  Activating postgresql96-server @9.6beta2_0

To create a database instance, after install do
 sudo mkdir -p /opt/local/var/db/postgresql96/defaultdb
 sudo chown postgres:postgres /opt/local/var/db/postgresql96/defaultdb
 sudo su postgres -c '/opt/local/lib/postgresql96/bin/initdb -D /opt/local/var/db/postgresql96/defaultdb'

--->  Cleaning postgresql96-server
--->  Computing dependencies for postgresql96
--->  Cleaning postgresql96
--->  Updating database of binaries
--->  Scanning binaries for linking errors
--->  No broken files found.

The log provides instructions on the rest of the steps for installation, so we do that next.

sudo mkdir -p /opt/local/var/db/postgresql96/defaultdb
sudo chown postgres:postgres /opt/local/var/db/postgresql96/defaultdb
sudo su postgres -c '/opt/local/lib/postgresql96/bin/initdb -D /opt/local/var/db/postgresql96/defaultdb'

Now we start the server:

sudo port load -w postgresql96-server

Verify that we can connect to the server:

su postgres -c psql

You will see a prompt from postgres:

psql (9.6.1)
Type "help" for help.

postgres=#

Here you can type a query to see that the server is running.

postgres=#SELECT setting FROM pg_settings WHERE name='data_directory';

And see the response: