Dont allow update on empty textbox in php

Question

Is it possible not to update mysql data if one of the textbox in an html form which will update the mysql data is empty?

Answer 1

if (!empty($_POST['nameOfTheTextBox'])) {
    // do sql update query
} else {
    echo "you need to enter a text";
}

Also as the comment to your question proposes I would strongly recommend to read about form validation/sanitizing