题解 | #牛客的课程订单分析(六)#

# 判断'is_group_buy'字段
select o.id, 
    o.is_group_buy, 
    case
        when o.is_group_buy = 'No' then c.name      -- 使用 CASE 表达式进行条件判断
        else NULL
    end as client_name
from order_info o left join client c    -- left join:只有非拼团(is_group_buy为No)订单
on o.client_id = c.id
where date > '2025-10-15' 
    and status = 'completed'
    and product_name in ('C++', 'Java', 'Python')
    and user_id in (                -- 要显示除了user_id的信息，不能直接使用group by后的结果，参考上一题
        select user_id
        from order_info
        where date > '2025-10-15' 
            and status = 'completed' 
            and product_name in ('C++', 'Java', 'Python')
        group by user_id
        having count(id) >= 2
    )
order by id;