SQL practice: SQL solves problems for X consecutive days

In the last section , Through the case of user retention , Explain the solution X The idea of the question of heaven , Next , In this section, let's take a look at continuity X God's question , This kind of problem is often needed to be solved in the interview and actual business .

First, the continuous indicators 、 Make a definition , as follows ：

• 1 Day after day ： After login on the same day , I logged in the next day , such as 2021.2.10 Logged in ,2021.2.11 Logged in is counted as 1 Day after day .
• 3 Day after day ： After login on the same day , On the second and third days, I also logged in , such as 2021.2.10 Logged in ,2021.2.11 and 2021.2.12 Logged in is counted as 3 Day after day .
• And so on ···

Now suppose , There is a user login form t_user_login, Field user_id and login_time Represent users respectively id And landing time . Next , We go through SQL To find continuity 3 Japan 、7 Users who log in on the th .

commonly , Solve such continuous problems X The idea of the heaven problem is as follows ：

• First step , You can use window functions to user_id Grouping sorting rn;
• The second step , Subtract the sequence number after sorting from the login time rn;
• The third step , If the dates are consecutive , The date will be the same .

below , We use a case to illustrate .

First , Let's build t_user_login surface .

DROP TABLE IF EXISTS `