左连接两个表，多列

Question

我需要左连接两个表：Cardealers 和 Applications。

我想看看哪些发牌商收到了哪些申请。

每个应用程序都转发给三个cardealers，因此我的表结构包含这 3 列：receiver_1、receiver_2、receiver_3。

接收者列中的 ID 与 cardealer_id 相同。

我有此代码仅适用于 ONE 和一列：

$res1 = $wpdb->get_results( " SELECT leads.*, cardealers.*
    FROM leads
    LEFT JOIN cardealers ON leads.receiver_1 = cardealers.cardealer_id
    WHERE leads.receiver_1 = cardealers.cardealer_id
    AND cardealers.cardealer_id = '". $cardealer_id ."'" );

$res2 = $wpdb->get_results( " SELECT leads.*, cardealers.*
    FROM leads
    LEFT JOIN cardealers ON leads.receiver_2 = cardealers.cardealer_id
    WHERE leads.receiver_2 = cardealers.cardealer_id
    AND cardealers.cardealer_id = '". $cardealer_id ."'" ); 

$res3 = $wpdb->get_results( " SELECT leads.*, cardealers.*
    FROM leads
    LEFT JOIN cardealers ON leads.receiver_3 = cardealers.cardealer_id
    WHERE leads.receiver_3 = cardealers.cardealer_id
    AND cardealers.cardealer_id = '". $cardealer_id ."'" );

如您所见，我做了 3 个单独的语句，它们都有效。但我想将这些组合成一个声明。

我该怎么做？

Answer 1

只需继续添加表格并为其命名。

SELECT 
   leads.*, cardealers1.*, cardealers2.*, cardealers3* 
FROM leads 
LEFT JOIN cardealers as cardealers1
   ON leads.receiver_1 = cardealers1.cardealer_id 
LEFT JOIN cardealers as cardealers2
   ON leads.receiver_2 = cardealers2.cardealer_id
LEFT JOIN cardealers as cardealers3
   ON leads.receiver_3 = cardealers3.cardealer_id
WHERE 
   leads.receiver_1 = cardealers1.cardealer_id 
   AND leads.receiver_2 = cardealers2.cardealer_id 
   AND leads.receiver_3 = cardealers3.cardealer_id 
   AND cardealers.cardealer_id = '". $cardealer_id ."'

编辑：最好为每个cardealers的列提供别名