How can undefined variables be avoided when working with PHP scripts that interact with MySQL databases?

To avoid undefined variables when working with PHP scripts that interact with MySQL databases, always check if variables are set before using them. This can be done using the isset() function in PHP. By checking if variables are set before using them, you can prevent errors that may occur when trying to access undefined variables.

// Check if the variable is set before using it
if(isset($variable_name)){
    // Use the variable here
    echo $variable_name;
} else {
    // Handle the case when the variable is not set
    echo "Variable is not set";
}