Question

我有这个内部查询，选择链接到给予者用户的所有分支机构。

 (SELECT 
    `realtor_user_id`
 FROM
    `affiliate_assignments`
 WHERE
 `lender_user_id` = `users`.`id`)

affiliate_assignments结构是：

id | realtor_user_id | lender_user_id

其中users表在外部查询中加入，realtor_user_id和lender_user_id都是users.id的外键

我还有用户的role（在外部查询中选择），可以是realtor或lender

我需要的是：

IF role = 'lender'

 SELECT realtor_user_id 
 FROM affiliate_assignments
 WHERE lender_user_id = users.id

ELSE IF role = 'realtor'

 SELECT lender_user_id
 FROM affiliate_assignments
 WHERE realtor_user_id = users.id

END IF

如何实现这一目标？

Answer 1

时可以使用案例

    select case when role = 'lender' then realtor_user_id 
                when role = 'realtor'  then lender_user_id 
            end  as my_result 
    FROM affiliate_assignments
    WHERE lender_user_id = users.id

事实上你有不同的条件你可以使用复合条件重建你的条件是when子句

select  case  
            when role = 'lender'  AND lender_user_id = users.id  then realtor_user_id 
            when  role = 'realtor' AND realtor_user_id = users.id then lender_user_id
                  ELSE  your_result_for else 
FROM affiliate_assignments

Answer 2

使用案例陈述：

SELECT CASE
    WHEN role = 'lender' THEN realtor_user_id
    WHEN role = 'realtor' THEN lender_user_id
    END CASE 
FROM affiliate_assignments
WHERE realtor_user_id = users.id

Answer 3

解决此问题的一种方法是使用left join s：

select u.*,
       coalesce(aal.realtor_user_id, aar.lender_user_id) as other_user_id
from users u left join
     affiliate_assignments aal
     on u.id = aal.lender_user_id and u.role = 'lender' left join
     affiliate_assignments aar
     on u.id = aar.realtor_user_id and u.role = 'realtor';

查询

3 个答案: