php - 使用一个查询进行多个求和查询

Question

我想根据产品表中的产品信息和产品历史表中的某些字段进行集合，如何在单个查询中执行此操作？

我的示例代码:

    <table> 
    <thead> 
        <tr> 
            <th>Product</th>
            <th>Model</th>
            <th>Actıve Total</th>
            <th>Pasıve Total</th>
            <th>Color Total</th>
        </tr> 
    </thead> 
    <tbody> 
<?php 

$product = $db->get_results("SELECT * FROM product WHERE (status='ACTIVE')");


foreach ($product as $p ){

$active_total   = $db->get_var("SELECT SUM(price) FROM product_history WHERE pid='$p->pid' AND status='AKTIVE'");
$pasive_total   = $db->get_var("SELECT SUM(price) FROM product_history WHERE pid='$p->pid' AND status='PASIVE'");
$color_total    = $db->get_var("SELECT SUM(price) FROM product_history WHERE pid='$p->pid' AND status='ACTIVE' AND color='BLUE'");
?>      
        <tr> 
            <td><?php echo $p->name; ?></td>
            <td><?php echo $p->model; ?></td> 
            <td><?php echo $active_total; ?></td> 
            <td><?php echo $pasive_total; ?></td> 
            <td><?php echo $color_total; ?></td>
         </tr> 
<?php } ?>
    </tbody> 
</table>

谢谢。

Answer 1

您可以使用条件聚合从一个查询中获取这些结果:

$sql = "SELECT
            SUM(CASE WHEN status='AKTIVE' THEN price ELSE 0 END) AS aktive,
            SUM(CASE WHEN status='PASIVE' THEN price ELSE 0 END) AS pasive,
            SUM(CASE WHEN status='AKTIVE' AND color='BLUE' THEN price ELSE 0 END) AS color,
        FROM product_history 
        WHERE pid='$p->pid'");

您实际上可以使用LEFT JOIN将两个查询合并为1。 :

$sql = "SELECT p.*,
               SUM(CASE WHEN h.status='AKTIVE' THEN h.price ELSE 0 END) AS aktive,
               SUM(CASE WHEN h.status='PASIVE' THEN h.price ELSE 0 END) AS pasive,
               SUM(CASE WHEN h.status='AKTIVE' AND h.color='BLUE' THEN h.price ELSE 0) AS color
        FROM product p
        LEFT JOIN product_history h ON h.pid = p.pid
        WHERE p.status='ACTIVE'
        GROUP BY p.pid";

如果唯一感兴趣的值来自 product是 pid (为了匹配 pid 中的 product_history 值)您应该更改 p.*在查询 p.pid 中。否则，理想情况下您应该枚举您想要其值的特定字段。参见 Why is SELECT * considered harmful?