SQL查询中如何根据attached_document列是否为空显示不同值？

select 
    ev.actual_date, 
    ev.event_name, 
    ev.generic_description, 
    ev.full_name as client_name, 
    ev.staff_desc as staff, 
    ev.user_entered_desc as entered_by,
    -- 处理attached_document列的判断逻辑
    CASE 
        WHEN ev.attached_document IS NULL THEN 'No attachment'
        ELSE 'has attachment'
    END as attachment_status
from event_view ev 
where event_name in
('Treatment Plan', 'Treatment Plan Rev.2', 'Treatment Plan Review',
'Treatment Plan Review Rev.2') 
and is_service_event = '1' 
order by event_name, actual_date, client_name

逻辑说明 #

用标准SQL的CASE语句实现需求：

• 当attached_document的值为NULL时，返回'No attachment'
• 当列存在非空值时，返回'has attachment'
• 给处理后的列起别名attachment_status，便于后续识别使用

内容的提问来源于stack exchange，提问作者Orderkonnect