What are the potential pitfalls of using nested queries in PHP to retrieve data from a database?

Potential pitfalls of using nested queries in PHP to retrieve data from a database include decreased performance due to multiple queries being executed, increased complexity of the code which may lead to harder maintenance, and the risk of SQL injection if not handled properly. To solve this issue, it is recommended to use JOIN clauses in SQL queries to combine related tables and retrieve the desired data in a single query. 

// Example of using JOIN in SQL query to retrieve data from multiple tables
$query = "SELECT users.username, orders.order_date
          FROM users
          JOIN orders ON users.id = orders.user_id
          WHERE users.id = 1";

$result = mysqli_query($connection, $query);

if(mysqli_num_rows($result) > 0) {
    while($row = mysqli_fetch_assoc($result)) {
        echo "Username: " . $row['username'] . " - Order Date: " . $row['order_date'] . "<br>";
    }
} else {
    echo "No results found.";
}

Keywords

nested queries database retrieval PHP performance SQL injection

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