After I did brew update and brew upgrade, my postgres got some problem. I tried to uninstall postgres and install again, but it didn't work as well.

This is the error message.(I also got this error message when I try to do rake db:migrate)

$ psql
psql: could not connect to server: No such file or directory
    Is the server running locally and accepting
    connections on Unix domain socket "/tmp/.s.PGSQL.5432"?

How can I solve it?

Mac version: Mountain lion.

homebrew version: 0.9.3

postgres version: psql (PostgreSQL) 9.2.1

And this is what I did.

12:30 ~/D/works$ brew uninstall postgresql
Uninstalling /usr/local/Cellar/postgresql/9.2.1...
12:31 ~/D/works$ brew uninstall postgresql
Uninstalling /usr/local/Cellar/postgresql/9.1.4...
12:31 ~/D/works$ psql --version
bash: /usr/local/bin/psql: No such file or directory
12:33 ~/D/works$ brew install postgresql
==> Downloading http://ftp.postgresql.org/pub/source/v9.2.1/postgresql-9.2.1.tar.bz2
Already downloaded: /Library/Caches/Homebrew/postgresql-9.2.1.tar.bz2
......
......
==> Summary
/usr/local/Cellar/postgresql/9.2.1: 2814 files, 38M, built in 2.7 minutes
12:37 ~/D/works$ initdb /usr/local/var/postgres -E utf8
The files belonging to this database system will be owned by user "laigary".
This user must also own the server process.

The database cluster will be initialized with locale "en_US.UTF-8".
The default text search configuration will be set to "english".

initdb: directory "/usr/local/var/postgres" exists but is not empty
If you want to create a new database system, either remove or empty
the directory "/usr/local/var/postgres" or run initdb
with an argument other than "/usr/local/var/postgres".
12:39 ~/D/works$ mkdir -p ~/Library/LaunchAgents
12:39 ~/D/works$   cp /usr/local/Cellar/postgresql/9.2.1/homebrew.mxcl.postgresql.plist ~/Library/LaunchAgents/
12:39 ~/D/works$   launchctl load -w ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist
homebrew.mxcl.postgresql: Already loaded
12:39 ~/D/works$ pg_ctl -D /usr/local/var/postgres -l /usr/local/var/postgres/server.log start
server starting
12:39 ~/D/works$ env ARCHFLAGS="-arch x86_64" gem install pg
Building native extensions.  This could take a while...
Successfully installed pg-0.14.1
1 gem installed
12:42 ~/D/works$ psql --version
psql (PostgreSQL) 9.2.1
12:42 ~/D/works$ psql
psql: could not connect to server: No such file or directory
    Is the server running locally and accepting
    connections on Unix domain socket "/tmp/.s.PGSQL.5432"?