返回Mysqli execute（）的结果

So $stmt->execute(); => returns a bool value, whether your query was successfully executed or not, and you can do it simply like this:

function delete_cat($category){
    $stmt = $mysqli->prepare("DELETE category, products FROM category INNER JOIN products WHERE category.id = ? AND product_cat = category.category_name ");
    $stmt->bind_param($category);
    $result = $stmt->execute();
    $stmt->close();
   return $result;
}

If you needed to get the count of the deleted elements, you can use mysqli_stmt_affected_rows, something like this:

function delete_cat($category){
    $stmt = $mysqli->prepare("DELETE category, products FROM category INNER JOIN products WHERE category.id = ? AND product_cat = category.category_name ");
    $stmt->bind_param($category);
    $stmt->execute();
    $result = $stmt->affected_rows;
    $stmt->close();
   return $result;
}

function delete_cat($category){
    $stmt = $mysqli->prepare("DELETE category, products FROM category INNER JOIN products WHERE category.id = ? AND product_cat = category.category_name ");
    $stmt->bind_param($category);
    $result = $stmt->execute(); // store the return of the method into a variable here so we can return it later
    $stmt->close();
    return $result // would return if the rows have been deleted or not.
    return $mysqli->affected_rows; // would return the amount of rows deleted

}

If you want to get the amount of rows that have been deleted you use affected_rows, if you want to just get the result if the SQL query was performed succesfull, simply store the return of $stmt->execute into a variable and return that.

http://php.net/manual/en/mysqli-stmt.affected-rows.php

http://php.net/manual/de/mysqli-stmt.execute.php