用PHP語言計算SQL中的演繹？

Question

我想要什麼：「收入總數 - 總開支總數=左」

我仍然無法讓代碼來計算扣款，請幫我解下面的代碼，謝謝。

<?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 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 

Answer 2

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