diff --git a/db/source.sql b/db/source.sql
index c5f6fcd..88dc23f 100644
--- a/db/source.sql
+++ b/db/source.sql
@@ -1,20 +1,20 @@
 BEGIN TRANSACTION;
 CREATE TABLE IF NOT EXISTS "registry" (
 	"id"	INTEGER NOT NULL UNIQUE,
-	"domain"	TEXT,
-	"username"	TEXT,
+	"domain"	TEXT NOT NULL UNIQUE,
+	"username"	TEXT NOT NULL,
 	"last_renewal"	INTEGER,
 	PRIMARY KEY("id" AUTOINCREMENT)
 );
 CREATE TABLE IF NOT EXISTS "zones" (
 	"id"	INTEGER NOT NULL UNIQUE,
-	"zone"	TEXT NOT NULL,
+	"zone"	TEXT NOT NULL UNIQUE,
 	"username"	TEXT NOT NULL,
 	PRIMARY KEY("id" AUTOINCREMENT)
 );
 CREATE TABLE IF NOT EXISTS "users" (
 	"id"	INTEGER NOT NULL UNIQUE,
-	"username"	TEXT NOT NULL,
+	"username"	TEXT NOT NULL UNIQUE,
 	"password"	TEXT NOT NULL,
 	"registration_date"	INTEGER NOT NULL,
 	PRIMARY KEY("id" AUTOINCREMENT)
@@ -23,7 +23,7 @@ CREATE TABLE IF NOT EXISTS "sites" (
 	"id"	INTEGER NOT NULL UNIQUE,
 	"username"	TEXT NOT NULL,
 	"site_dir"	TEXT NOT NULL,
-	"domain"	TEXT NOT NULL,
+	"domain"	TEXT NOT NULL UNIQUE,
 	"domain_type"	TEXT NOT NULL,
 	"protocol"	TEXT NOT NULL,
 	"creation_date"	INTEGER NOT NULL,
diff --git a/fn/auth.php b/fn/auth.php
index e428c82..de957af 100644
--- a/fn/auth.php
+++ b/fn/auth.php
@@ -29,55 +29,24 @@ function hashPassword($password) {
 }
 
 function userExist($username) {
-	$usernameArray[0] = $username;
-
-	$db = new PDO('sqlite:' . DB_PATH);
-
-	$op = $db->prepare('SELECT username FROM users WHERE username = ?');
-	$op->execute($usernameArray);
-
-	$data = $op->fetch();
-	if (isset($data['username']))
-		return true;
-	else
-		return false;
+	return $username === query('select', 'users', ['username' => $username], 'username')[0];
 }
 
 function checkPassword($username, $password) {
-	$username2[0] = $username;
-
-	$db = new PDO('sqlite:' . DB_PATH);
-
-	$op = $db->prepare('SELECT username, password FROM users WHERE username = ?');
-	$op->execute($username2);
-
-	$dbPassword = $op->fetch()['password'];
-
-	return password_verify($password, $dbPassword);
+	return password_verify($password, query('select', 'users', ['username' => $username], 'password')[0]);
 }
 
 function outdatedPasswordHash($username) {
-	$username2[0] = $username;
-
-	$db = new PDO('sqlite:' . DB_PATH);
-
-	$op = $db->prepare('SELECT username, password FROM users WHERE username = ?');
-	$op->execute($username2);
-
-	$dbPassword = $op->fetch()['password'];
-
-	return password_needs_rehash($dbPassword, ALGO_PASSWORD, OPTIONS_PASSWORD);
+	return password_needs_rehash(query('select', 'users', ['username' => $username], 'password')[0], ALGO_PASSWORD, OPTIONS_PASSWORD);
 }
 
 function changePassword($username, $password) {
-	$password = hashPassword($password);
-
 	$db = new PDO('sqlite:' . DB_PATH);
 
 	$stmt = $db->prepare("UPDATE users SET password = :password WHERE username = :username");
 
 	$stmt->bindValue(':username', $username);
-	$stmt->bindValue(':password', $password);
+	$stmt->bindValue(':password', hashPassword($password));
 
 	$stmt->execute();
 }
diff --git a/fn/dns.php b/fn/dns.php
index 6476942..282aa2f 100644
--- a/fn/dns.php
+++ b/fn/dns.php
@@ -39,10 +39,9 @@ function checkAbsoluteDomainFormat($domain) {
 }
 
 function checkAction($action) {
-	if ($action === "delete")
-		return "un";
-	else if ($action === "add")
-		return "";
-	else
-		userError("Wrong value for action.");
+	return match ($action) {
+		'add' => '',
+		'delete' => 'un',
+		default => userError("Wrong value for action."),
+	};
 }
diff --git a/fn/reg.php b/fn/reg.php
index 5c5e423..693c2ad 100644
--- a/fn/reg.php
+++ b/fn/reg.php
@@ -6,17 +6,7 @@ function regGetUpperDomain($domain) {
 }
 
 function regListUserDomains($username) {
-	$db = new PDO('sqlite:' . DB_PATH);
-	$usernameArray[0] = $username;
-
-	$op = $db->prepare('SELECT domain FROM registry WHERE username = ?');
-	$op->execute($usernameArray);
-
-	$domains = [];
-	foreach ($op->fetchAll() as $domain)
-		array_push($domains, $domain['domain']);
-
-	return $domains;
+	return query('select', 'registry', ['username' => $username], 'domain');
 }
 
 function regCheckDomainPossession($domain) {
@@ -29,20 +19,8 @@ function regCheckDomainPossession($domain) {
 }
 
 function regIsFree($domain) {
+	foreach (query('select', 'registry', ['domain' => $domain], 'domain')) {
 
-	$domainArray[0] = $domain;
-
-	$db = new PDO('sqlite:' . DB_PATH);
-
-	$req = $db->prepare('SELECT domain FROM registry WHERE domain = ?');
-	$req->execute($domainArray);
-
-	$data = $req->fetch();
-
-	if (isset($data['domain'])) {
-		return false;
-	} else {
-		return true;
 	}
 
 }