How can the issue of data duplication in a database be efficiently addressed using PHP code?

Data duplication in a database can be efficiently addressed by implementing a unique constraint on the database table columns that should not contain duplicate values. This constraint will prevent any new data from being inserted if it violates the uniqueness rule, thereby eliminating the issue of data duplication.

// Example PHP code to add a unique constraint to a database table column
$sql = "ALTER TABLE table_name ADD CONSTRAINT unique_constraint_name UNIQUE (column_name)";
$result = mysqli_query($conn, $sql);

if ($result) {
    echo "Unique constraint added successfully.";
} else {
    echo "Error adding unique constraint: " . mysqli_error($conn);
}