How to run 2 sql queries in one php if statement?

This is the code i have so far

if (isset($_POST['button1']))
    {
        $sql = "DELETE FROM UpcomingRota";
        $E1 = $_POST["MondayAMFirstEmployee"]; $E2 = $_POST["MondayAMSecondEmployee"]; $E3 = $_POST["MondayAMThirdEmployee"];
        $sql = "INSERT INTO UpcomingRota (DayAndTime, FirstEmployee, SecondEmployee, ThirdEmployee) VALUES ('MondayAM', '$E1', '$E2', '$E3')";

    }

Both the $sql statements work perfectly on there own but when i have both in the if statement it seems to bypass the first one and just run the last $sql statement.

How can i get it to run as many $sql statements as i need it to.... going to have around 15 - 20 in there.

Thanks in advance.