Condition with SQL

Good morning, everyone,

I've come to see you for a question. Is there a condition in SQL that allows you to do that:
IF(sup = void) {
}

Database
id | nom | prenom |    lieu    |               mail                   |        fixe        |     image    | sup
1 | Paul |    Doss   | France | exemple@exemple.com| 0200000000 | defaut.img | (vide)

Thank you for your help.