What is the difference between using isset() and empty() in PHP for variable validation?

When validating variables in PHP, isset() is used to check if a variable is set and not null, while empty() is used to check if a variable is empty or not. It's important to use isset() when you want to ensure that a variable exists before checking its value, and use empty() when you want to check if a variable has a non-empty value.

// Using isset() to validate a variable
if(isset($variable)){
    // Variable is set and not null
}

// Using empty() to validate a variable
if(!empty($variable)){
    // Variable is not empty
}