CREATE DATABASE IF NOT EXISTS in PostgreSQL

Hi, hackers

When I try to use CREATE DATABASE IF NOT EXISTS in PostgreSQL, it complains
this syntax is not supported.  We can use the following command to achieve
this, however, it's not straightforward.

     SELECT 'CREATE DATABASE mydb'
     WHERE NOT EXISTS (SELECT FROM pg_database WHERE datname = 'mydb')\gexec

Why don't support CREATE DATABASE IF NOT EXISTS syntax in PostgreSQL?

I create a patch for this, any suggestions?

-- 
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.