mysql_fetch_array不显示结果当我在php中使用连接表

Question

我已经做了一个像发票的软件。现在我想显示股票的具体结果。例如每次购买和出售很多次的产品（总购买总销售额=股票）。我使用下面的代码时，我使用一个表和测试总和功能的出售或再见它的工作，但多表不工作？

buy: 
id name  detail pquantity unitprice 
1 Laptop Samsung  3   $150 
2 Keyboard Perfect  6   $5 
3 Monitor dell  2   $60 
4 Laptop Samsung  2   $150 

sell 
id name  detail iquantity unitprice 
1 Laptop Samsung  1   $180 
2 Keyboard Perfect  1   $6 
3 Laptop Samsung  2   $170 


//mysql query 
$result= mysql_query("SELECT pname,pdetails, SUM(pquantity) - SUM(iquantity) AS stock FROM 
buy INNER JOIN sell GROUP BY pname,pdetails"); 

//for display 
while ($row=mysql_fetch_array($result)){ 
$itemname=$row['pname']; 
$details=$row['pdetails']; 
$pquantity=$row['pquantity']; 
$iquantity =$row['iquantity']; 
$cstock =$row['stock']; 
echo "<tr>"; 

echo "<td>$itemname</td>"; 
echo "<td>$details</td>"; 
echo "<td>$pquantity</td>"; 
echo "<td>$iquantity</td>"; 
echo "<td>$cstock</td>"; 
echo "</tr>"; 

} 

Answer 1

在inner join你需要指定的内部条件从主表和其他表之间不匹配行。在你的情况下：

SELECT pname, pdetails, SUM(pquantity) - SUM(iquantity) AS stock FROM 
    buy b INNER JOIN sell s on s.id = b.id GROUP BY pname, pdetails;