用PHP語言計算SQL的扣除額？

Question

我想要的是：“總收入-總支出=剩余”

我仍然無法使代碼計算得出，請幫助我解決下面的代碼，非常感謝。

    <?php
       include("connect-db.php");
       $left= mysql_query("Select income.inNo,expenses.eNo 
                          From income Join expenses On income.uId = expenses.uId")
       while($row = mysql_fetch_array($left))
     {
       echo "Left: RM".$row['SUM(inNo)'] - $row['SUM(eNo)'];
     }
    ?>

Answer 1

Select SUM(income.inNo) AS inc, SUM(expenses.eNo) AS exp,
SUM(income.inNo) - SUM(expenses.eNo) AS Leftover  
FROM income 
JOIN expenses On income.uId = expenses.uId

Answer 2

SELECT income - expense AS LEFT
FROM (SELECT SUM(inNo) AS income
      FROM income) AS i
CROSS JOIN (SELECT SUM(eNo) AS expense
            FROM expense) AS e