What are the differences between using "Count" and "Count(distinct)" in a PHP MySQL query, and when should each be used?

When using "Count" in a MySQL query, it will count all rows that match the specified condition, including duplicates. On the other hand, "Count(distinct)" will only count unique values, eliminating duplicates from the count. Use "Count" when you want to count all occurrences of a specific condition, including duplicates. Use "Count(distinct)" when you want to count only unique occurrences of a specific condition. Example PHP code snippet:

// Using Count to count all rows
$query = "SELECT COUNT(id) FROM table_name WHERE condition";
$result = mysqli_query($connection, $query);
$row = mysqli_fetch_array($result);
echo "Total count: " . $row[0];

// Using Count(distinct) to count unique values
$query = "SELECT COUNT(DISTINCT column_name) FROM table_name WHERE condition";
$result = mysqli_query($connection, $query);
$row = mysqli_fetch_array($result);
echo "Unique count: " . $row[0];