左聯接兩個表，多列

Question

我需要加入兩個表： Cardealers和Applications 。

我想看看哪些cardealers收到了哪些申請。

每個應用程序被轉發到三個cardealers因而我的表結構具有這些3列： receiver_1 ， receiver_2 ， receiver_3 。

接收方列中的ID與cardealer_id相同。

我的這段代碼僅適用於一列：

$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 ."'" );

如您所見，我執行了3個獨立的語句，所有語句均有效。 但我想將這些合並為一個陳述。

我該怎么做呢？

Answer 1

只需繼續添加表並為其別名。

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 ."'

編輯：最好為每個cardealers的列提供別名