diff --git a/addAction.php b/addAction.php
index a02900d..034e2bc 100644
--- a/addAction.php
+++ b/addAction.php
@@ -28,17 +28,33 @@
 			echo "<font color='red'>Email field is empty.</font><br/>";
 		}
 		
+		// Show link to the previous page
+		echo "<br/><a href='javascript:self.history.back();'>Go Back</a>";
+	} elseif (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
+		echo "<font color='red'>The email address '$email' is considered invalid.</font><br/>";
+
 		// Show link to the previous page
 		echo "<br/><a href='javascript:self.history.back();'>Go Back</a>";
 	} else { 
 		// If all the fields are filled (not empty) 
 
-		// Insert data into database
-		$result = mysqli_query($mysqli, "INSERT INTO users (`name`, `age`, `email`) VALUES ('$name', '$age', '$email')");
-		
-		// Display success message
-		echo "<p><font color='green'>Data added successfully!</p>";
-		echo "<a href='index.php'>View Result</a>";
+		try {
+			// Insert data into database
+			$result = mysqli_query($mysqli, "INSERT INTO users (`name`, `age`, `email`) VALUES ('$name', '$age', '$email')");
+
+			// Kalau query berhasil, tampilkan success message
+			if ($result) {
+				echo "<p><font color='green'>Data added successfully!</font></p>";
+				echo "<a href='index.php'>View Result</a>";
+			}
+
+		} catch (mysqli_sql_exception $e) {
+			if ($e->getCode() == 1062) { // 1062 = Duplicate entry
+				echo "Email must be unique.";
+				echo "<br/><a href='javascript:self.history.back();'>Go Back</a>";
+			}
+		}
+
 	}
 }
 ?>
diff --git a/database.sql b/database.sql
index aeb4ffb..8b21b6f 100644
--- a/database.sql
+++ b/database.sql
@@ -6,6 +6,6 @@ CREATE TABLE `users` (
   `id` int(11) NOT NULL auto_increment,
   `name` varchar(100) NOT NULL,
   `age` int(3) NOT NULL,
-  `email` varchar(100) NOT NULL,
+  `email` varchar(100) UNIQUE NOT NULL,
   PRIMARY KEY  (`id`)
 );
\ No newline at end of file
diff --git a/editAction.php b/editAction.php
index 5b0cc75..b6f112a 100644
--- a/editAction.php
+++ b/editAction.php
@@ -22,12 +22,32 @@
 		if (empty($email)) {
 			echo "<font color='red'>Email field is empty.</font><br/>";
 		}
+
+		// Show link to the previous page
+		echo "<br/><a href='javascript:self.history.back();'>Go Back</a>";
+	} elseif (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
+		echo "<font color='red'>The email address '$email' is considered invalid.</font><br/>";
+
+		// Show link to the previous page
+		echo "<br/><a href='javascript:self.history.back();'>Go Back</a>";
 	} else {
-		// Update the database table
-		$result = mysqli_query($mysqli, "UPDATE users SET `name` = '$name', `age` = '$age', `email` = '$email' WHERE `id` = $id");
-		
-		// Display success message
-		echo "<p><font color='green'>Data updated successfully!</p>";
-		echo "<a href='index.php'>View Result</a>";
+
+		try {
+			// Update the database table
+			$result = mysqli_query($mysqli, "UPDATE users SET `name` = '$name', `age` = '$age', `email` = '$email' WHERE `id` = $id");
+
+			// Kalau query berhasil, tampilkan success message
+			if ($result) {
+				// Display success message
+				echo "<p><font color='green'>Data updated successfully!</p>";
+				echo "<a href='index.php'>View Result</a>";
+			}
+
+		} catch (mysqli_sql_exception $e) {
+			if ($e->getCode() == 1062) { // 1062 = Duplicate entry
+				echo "Email must be unique.";
+				echo "<br/><a href='javascript:self.history.back();'>Go Back</a>";
+			}
+		}
 	}
 }