Php 我怎样才能从两张表中减去

我想从收入总额表中减去支出总额，但每次运行查询时都会得到错误的数字

<?php
$query="SELECT income.Source
          ,SUM(income.Amount) as in_Amount
          ,SUM(expenses.Amount) as out_Amount
          ,SUM(income.Amount) - SUM(expenses.Amount) as total 
        FROM income as income
          , expenses";

$result=mysql_query($query);

while($row=mysql_fetch_array($result)){
    echo '<p class="stat"><span class="label label-danger">' . $row['total']. '</span> Naira Net Income</p>';
}
?>

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收入表总共有40000个，而费用表总共有5000个，查询结果是30000个。

如果要进行连接，则应该进行子查询。试试这个：

<?php
$query="SELECT income.Source
          ,SUM(income.Amount) as in_Amount
          ,SUM(expenses.Amount) as out_Amount
          ,SUM(income.Amount) - SUM(expenses.Amount) as total 
        FROM income as income
          , expenses";

$result=mysql_query($query);

while($row=mysql_fetch_array($result)){
    echo '<p class="stat"><span class="label label-danger">' . $row['total']. '</span> Naira Net Income</p>';
}
?>

SELECT Source, in_Amount, out_Amount, total_income - total_expenses FROM
(
  SELECT income.Source, SUM(income.Amount) as in_Amount,   SUM(expenses.Amount) as out_Amount,
  ( SELECT SUM(income.Amount) ) AS total_income,
  ( SELECT SUM(expenses.Amount) ) AS total_expenses
  FROM income as income, expenses
) t

---

表收入和支出是相关的？是的，但是两个不同的表这两个表是如何相关的？哪一列可以与收入行和支出行关联？