php - 左连接两个表，多列

Question

我需要左连接两个表:Cardealers 和Applications。

我想查看哪些信用卡经销商收到了哪些申请。

每个申请都会转发给三个发卡商，因此我的表结构具有以下 3 列:receiver_1、receiver_2、receiver_3。

接收者列中的 ID 与 cardealer_id 相同。

我的这段代码仅适用于一列:

$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 ."'" );

正如你所看到的，我做了 3 个单独的语句，它们都有效。但我想将这些合并成一个声明。

我该怎么做？

Answer 1

只需继续添加表并为其添加别名即可。

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:最好为每个卡经销商的列指定一个别名