Fetch the user: MySql vs CouchDB

a_mysql-select.sql

SELECT `*` FROM `users` WHERE `username` = "[email protected]" AND `password` = "xxx"

b_couch-select.js

// design document
{
	"_id": "_design/user",
	"_rev": ... something ...,
	"language": "javascript",
	"views": {
		"credentials": {
			"map": "function (doc) {
					if (doc.type == 'user') {
						emit([doc.username, doc.password], null);
					}
				}"
		}
	}
}

// user document
{
	"_id": ... something ...,
	"_rev": ... something ...,
	"type": "user",
	"username": "[email protected]",
	"password": "xxx"
}

// http://127.0.0.1:5984/db_name/_design/user/_view/credentials?key=["[email protected]","xxx"]&include_docs=true