题解 | #计算用户8月每天的练题数量#

# 当作日期处理
# 1
SELECT  DAY(date) as day,count(device_id) as question_cnt
FROM question_practice_detail
WHERE DATE_FORMAT(date,'%Y-%m') = '2021-08'
group by DAY(date)

# #2
SELECT DAY(date) as day,count(device_id) as question_cnt
FROM question_practice_detail
WHERE YEAR(date) = '2021' and MONTH(date) = '8'
group by DAY(date)

# # 当做字符串处理
# # 1
SELECT DAY(date) as day,count(device_id) as question_cnt
FROM question_practice_detail
where substring_index(date,'-',2) = '2021-08'
group by DAY(date)

# # 2
SELECT DAY(date) as day,count(device_id) as question_cnt
FROM question_practice_detail
where LEFT(date,7) = '2021-08'
group by DAY(date)

# 3
SELECT DAY(date) as day,count(device_id) as question_cnt
FROM question_practice_detail
where date regexp('^2021-08')
group by DAY(date)