now

返回当前系统日期+时间,例如2023-07-26 16:06:28

select now();

curdate()

返回当前的系统日期,不包含时间,例如2023-07-26

select curdate()

此函数的作用与current_date变量作用一致

curtime

返回当前的系统时间,不包含日期,例如16:07:02

select curtime()

此函数的作用与current_time变量一致

通过的代码

SELECT
    s.name,
    today.cnt
FROM 
    subject s
JOIN (
    SELECT
        subject_id,
        count(*) as cnt
    FROM
        submission
    WHERE 
        create_time = current_date
    GROUP BY subject_id
) as today ON s.id = today.subject_id
ORDER BY today.cnt DESC, s.id