回答です

answer/Ex05_query.php

@@ -0,0 +1,25 @@
+<?php
+// Ex05_query.php
+
+function getJoinData()
+{
+    $dsn = "mysql:host=localhost;dbname=employee_db;charset=utf8";
+    $username = "rezouser";
+    $password = "Rezo_0000";
+    try {
+        $pdo = new PDO($dsn, $username, $password);
+        $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
+
+        $sql = "SELECT e.name AS employee_name, d.department_name, p.project_name
+                FROM employees e
+                JOIN departments d ON e.dep_id = d.id
+                JOIN projects p ON e.project_id = p.id";
+        $stmt = $pdo->query($sql);
+        $result = $stmt->fetchAll(PDO::FETCH_ASSOC);
+        return $result;
+    } catch (PDOException $e) {
+        return [];
+    } finally {
+        $pdo = null;
+    }
+}