MySQL查询帮助，按时间分组，查看记录是否已设置

Quick question on how to do this, I'm unsure how it would work. Essentially I have a table with thousands of rows per day, and I want to group them by date for each row. That part is easy, but then I want to know if an instance is in that group, for example I want to know if Paul is on this date.Quick question on how to do this, I'm unsure ho