What debugging techniques can be used to identify and resolve issues with SQL queries in PHP?

One common debugging technique to identify and resolve issues with SQL queries in PHP is to use error reporting functions such as mysqli_error() or PDO::errorInfo() to display any errors that occur during query execution. Additionally, you can echo or var_dump the SQL query itself to ensure it is being constructed correctly with the expected values.

// Example of using mysqli_error() to display SQL query errors
$query = "SELECT * FROM users WHERE id = $user_id";
$result = mysqli_query($conn, $query);

if (!$result) {
    echo "Error: " . mysqli_error($conn);
}

// Example of echoing the SQL query for debugging
$query = "SELECT * FROM users WHERE id = $user_id";
echo $query;
$result = mysqli_query($conn, $query);