Use MacPorts install PostgreSQL server

 sudo port install postgresql93-server

Create Database Instance

 sudo mkdir -p /opt/local/var/db/postgresql93/defaultdb  
 sudo chown postgres:postgres /opt/local/var/db/postgresql93/defaultdb  
 sudo su postgres -c '/opt/local/lib/postgresql93/bin/initdb -D /opt/local/var/db/postgresql93/defaultdb'  
 sudo mkdir -p /opt/local/var/log/postgresql  
 sudo chown postgres:postgres /opt/local/var/log/postgresql  

Start Database Server

 sudo su postgres -c '/opt/local/lib/postgresql93/bin/postgres -D /opt/local/var/db/postgresql93/defaultdb'  

or

 sudo su postgres -c '/opt/local/lib/postgresql93/bin/pg_ctl -D /opt/local/var/db/postgresql93/defaultdb -l /opt/local/var/log/postgresql/postgres.log start'

Set PATH environment variable

 export PATH=/opt/local/lib/postgresql93/bin:$PATH

Make sure you set the PostgreSQL path before /usr/bin to ensure that you are using the latest versions and not the default Apple provided, otherwise will encounter error when execute operation.

Create User

 createuser --superuser Chris -U postgres

Create Database

 createdb mydb

If below error encountered, that caused by you use old version PostgreSQL which provide by Apple, change PATH environment variable to solve.

  createdb: could not connect to database postgres: could not connect to server: No such file or directory   
     Is the server running locally and accepting
     connections on Unix domain socket "/var/pgsql_socket/.s.PGSQL.5432"?

Accessing Database

 psql mydb

mydb=# means you are a database superuser, otherwise display mydb=>.

Exit psql

 mydb=> \q

Shutdown Database Server

 sudo su postgres -c 'pg_ctl -D /opt/local/var/db/postgresql93/defaultdb -l /opt/local/var/log/postgresql/postgres.log stop'