将多个MySQL查询合并为1

Question

我试图显示一个汇总表，当前正在使用多个MySQL查询，我想知道是否有可能将它们组合为一个。

我有一个名为“付款”的表，其中包含金额和货币字段，并且我试图显示每种货币的汇总表。 举个例子：

<table>
  <tr>
    <td>USD</td>
    <td>EUR</td>
    <td>GBP</td>
  </tr>
  <tr>
  <? $q1 = mysqli_query("SELECT sum(amount) as total_USD from payments WHERE currency='USD'");
  while($row1 = mysqli_fetch_assoc($q1)){ ?>                
    <td><? echo number_format($row1['total_USD'],0); ?></td>
  <? } ?>

  <? $q2 = mysqli_query("SELECT sum(amount) as total_EUR from payments WHERE currency='EUR'");
  while($row2 = mysqli_fetch_assoc($q2)){ ?>                
    <td><? echo number_format($row2['total_EUR'],0); ?></td>
  <? } ?>

  <? $q3 = mysqli_query("SELECT sum(amount) as total_GBP from payments WHERE currency='GBP'");
  while($row3 = mysqli_fetch_assoc($q3)){ ?>                
    <td><? echo number_format($row3['total_GBP'],0); ?></td>
  <? } ?>
  </tr>
</table>

实际上，我使用的是12种货币，所以我有12个独立的查询，但是效率低下，所以我想知道是否有更简单的方法来获得相同的结果？

非常感谢！

Answer 1

SELECT currency,
       SUM(amount) as total
  FROM payments
 GROUP BY currency

Answer 2

     Solution 1:
       SELECT currency, SUM(amount) as total FROM payments GROUP BY currency
     Solution 2 :

   $currencies=array(USD,EUR,GBP,...);
    foreach($currencies as $currency){
      $q1= mysqli_query("SELECT sum(amount) as total from payments WHERE currency='".$currency."'");  
     while($row1 = mysqli_fetch_assoc($q1)){                
        echo number_format($row1['total'],0); 
       } 
    }

Answer 3

您可以在此处使用GROUP BY。

SELECT currency, SUM(amount) as total FROM payments GROUP BY currency

http://dev.mysql.com/doc/refman/5.1/en/group-by-modifiers.html