Mysql – Joins in MySQL database

No, you have not defined any Foreign key constraints.

The MySQL documentation page about FOREIGN KEY constraints has more details and possible options.

Here's an example for the invoices -> customers Foreign Key:

CREATE TABLE IF NOT EXISTS `nt_invoices` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `customer_id` int(11) NOT NULL,
  `owner_id` int(11) NOT NULL,
  `invoice_title` varchar(80) NOT NULL,
  `invoice_issue_date` date NOT NULL,
  `due_date` date NOT NULL,
  `description` text NOT NULL,
  `created_by` int(11) DEFAULT NULL,
  `updated_by` int(11) DEFAULT NULL,
  `created_at` datetime DEFAULT NULL,
  `updated_at` datetime DEFAULT NULL,
  PRIMARY KEY (`id`),

  KEY customer_id_index (customer_id),        --- index to be used by the FK

  CONSTRAINT customer_invoice_fk              --- the FK constraint's name
    FOREIGN KEY (customer_id)
      REFERENCES nt_customers(id)
      ON UPDATE CASCADE                       --- or other action
      ON DELETE RESTRICT                      --- here, too  

) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ;

If you look inside mongodb/bin folder (ls -l) You can find a couple of binaries.

The mongoDB has import and export tools.

If you're running mongod locally on the default port, you can just do:

$ ./mongodump

Example: Dumping Everything

$ ./mongodump --host prod.example.com

Example: Dumping a Single Collection

$ ./mongodump --db blog --collection posts

Others like

mongoexport, mongoimport, mongorestore, bsondump etc.

for more http://www.mongodb.org/display/DOCS/Import+Export+Tools