MYSQL连接错误。如何解决？

Question

MySQL查询：

SELECT * FROM `pet_info` LEFT JOIN `lostpets` ON `pet_info`.`id` = `lostpets`.`petid` LEFT JOIN `pet_images` ON `pet_info`.`id` = `pet_images`.`petid` LEFT JOIN ON `pet_info`.`pet_cat` CASE WHEN `pet_info`.`pet_cat` = 1 THEN `dog_breeds`.`id` WHEN `pet_info`.`pet_cat` = 2 THEN `cat_breeds`.`id` END WHERE `pet_info`.`pet_user_id` = 581 

错误：

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ON `pet_info`.`pet_cat` CASE WHEN `pet_info`.`pet_cat` = 1 THEN `do' at line 7 

为什么错误出现，请帮助我。 Gow可以解决这个错误吗？

Answer 1

下面是查询的格式化版本，突出显示了一些错误。

SELECT * 
    FROM pet_info p 
    LEFT 
    JOIN lostpets l 
    ON p.id = l.petid 
    LEFT 
    JOIN pet_images i 
    ON p.id = i.petid 
    LEFT 
    JOIN !! ERROR 1 
    ON p.pet_cat !! ERROR 2 
    CASE WHEN p.pet_cat = 1 
     THEN d.id !! ERROR 3 
     WHEN p.pet_cat = 2 
     THEN c.id END !! ERROR 4 
WHERE p.pet_user_id = 581