mysql - 在mysql中查询时如何从select case中获取值

Question

select     `event_attendees_mapping`.`attendees_status_id`
            FROM
                `event_attendees_mapping`
            WHERE
                ((`event_attendees_mapping`.`event_schedule_id` = 1)
                    AND (`event_attendees_mapping`.`employee_code` = 'TJU_741')                    
                    ) 

使用此查询，我可以获得在情况和条件下转换的值。

 select case     
           when (select     `event_attendees_mapping`.`attendees_status_id`
            FROM
                `event_attendees_mapping`
            WHERE
                ((`event_attendees_mapping`.`event_schedule_id` = 1)
                    AND (`event_attendees_mapping`.`employee_code` = 'TJU_741')                    
                    )  )then    1

                    else
                    0
                    end

但在这里，我在字段列表中收到错误未知表“event_attendees_mapping”，而从查询中我能够获取值，请告诉我哪里做错了，请建议我。

Answer 1

这是你想要的吗？

select     CASE WHEN `event_attendees_mapping`.`attendees_status_id` = ????
                THEN 1
                ELSE 0
           END as new_Col
FROM `event_attendees_mapping`
WHERE `event_attendees_mapping`.`event_schedule_id` = 1
  AND `event_attendees_mapping`.`employee_code` = 'TJU_741'