每日一SQL 【每月交易 I】

文章目录

• 问题
• 案例
• 执行顺序
• 使用分组解决

问题

案例

执行顺序

select，from，where，group by，order by，having， limit执行顺序

使用分组解决

select
    date_format(trans_date, '%Y-%m') as month,
    country,
    count(*) as trans_count,
    sum(state = 'approved') as approved_count,
    sum(amount) as trans_total_amount,
    sum(case when state = 'approved' then amount else 0 end) as approved_total_amount
from Transactions
group by date_format(trans_date, '%Y-%m'), country;

解释

date_format: 时间格式化函数

sum(case when...then...else...end): 对分组后的数据按照规则进行累计