What are the potential pitfalls of converting VARCHAR values to INT values for subtraction in a large table?

Converting VARCHAR values to INT values for subtraction in a large table can lead to data loss or incorrect results if the VARCHAR values contain non-numeric characters. To solve this issue, you should first validate the VARCHAR values to ensure they only contain numeric characters before converting them to INT values for subtraction. 

// Example code snippet to validate VARCHAR values before converting to INT for subtraction
$query = "SELECT column_name FROM table_name";
$result = mysqli_query($connection, $query);

while($row = mysqli_fetch_assoc($result)) {
    // Validate VARCHAR value to ensure it only contains numeric characters
    if(ctype_digit($row['column_name'])) {
        $int_value = (int)$row['column_name'];
        // Perform subtraction operation with INT value
        $result = $int_value - $another_int_value;
        echo $result;
    } else {
        echo "Invalid value for subtraction: " . $row['column_name'];
    }
}

Keywords

PHP VARCHAR INT conversion subtraction

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