I don't have any rewrite rule for this, my vhost configure is:

server {
server_name mysql.qumanyou.com;
root /var/www/myadmin;
include common_params;
}

where /var/www/admin is the folder containing phpmyadmin. The content for common_params:

listen 80;
#index index.html index.php;

error_page 500 502 503 504 /50x.html;
location = /50x.html {
root html;
}

error_page 404 /404.php;
location = /404.php {
root /var/www/errors;
include phpfcgi_params;
}

location / {
index index.html index.php;
}

location ~ \.php$ {
if (!-f $request_filename) {
return 404;
}
include phpfcgi_params;
}

The content of phpfcgi_params:

fastcgi_pass 127.0.0.1:9000;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
fastcgi_connect_timeout 300;
fastcgi_send_timeout 300;
fastcgi_read_timeout 300;
fastcgi_buffer_size 32k;
fastcgi_buffers 8 32k;
include fastcgi_params;

fastcgi_params is the default nginx fcgi configuration file.

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Thank you!