WHEREtemp.od=1

[550. Game Play Analysis IV](https://leetcode.com/problems/game-play-analysis-iv/)

WITH login_dateAS (SELECT player_id,MIN(event_date)AS first_login

FROM Activity

GROUP BY player_id),

recent_loginAS (

SELECT*, DATE_ADD(first_login, INTERVAL1 DAY)AS next_day

FROM login_date)

SELECT ROUND((SELECTCOUNT(DISTINCT(player_id))

FROM Activity

WHERE (player_id, event_date)IN

(SELECT player_id, next_dayFROM recent_login))/ (SELECTCOUNT(DISTINCT player_id)FROM Activity),2)AS fraction

[2356. Number of Unique Subjects Taught by Each Teacher](https://leetcode.com/problems/number-of-unique-subjects-taught-by-each-teacher)

SELECT teacher_id,COUNT(DISTINCT subject_id) cnt

FROM Teacher

GROUP BY teacher_id

[1141. User Activity for the Past 30 Days I](https://leetcode.com/problems/user-activity-for-the-past-30-days-i/)

SELECT activity_dateas day,COUNT(DISTINCT user_id)AS active_users

FROM Activity

WHERE activity_date BETWEEN DATE_SUB('2019-07-27', INTERVAL29 DAY)AND'2019-07-27'

GROUP BY activity_date

[1070. Product Sales Analysis III

SELECTs.product_id,s.yearAS first_year,s.quantity,s.price

FROM Sales s

JOIN (

SELECT product_id,MIN(year)AS year

FROM sales

GROUP BY product_id

) p

ONs.product_id=p.product_id

ANDs.year=p.year

WITH first_year_salesAS (

SELECTs.product_id,MIN(s.year)as first_year

FROM Sales s

INNER JOIN Product p

ONs.product_id=p.product_id

GROUP BYs.product_id)

SELECTf.product_id,f.first_year,s.quantity,s.price

FROM first_year_sales f

JOIN Sales s

ONf.product_id=s.product_id

ANDf.first_year=s.year