Find rows with consecutive dates

Question

Is it possible to know which customer came at the bar 3 consecutive days? (john in my case)

Thanks in advance

Name	Age	Date	Amount
Paul	12	2021-12-01	20
John	19	2021-12-01	10
Jack	17	2021-13-01	7
John	19	2021-13-01	8
John	19	2021-14-01	17

Answer 1

so I would approach this by

SELECT FROM Table
    LEFT JOIN Table As PrevDay on PrevDay.Customer = Table.Customer 
        AND PrevDay.date = DATEADD(DAY,-1,Table.Date)
    LEFT JOIN Table AS NextDay on NextDay,Customer = Table.Customer 
        AND NextDay.Date = DATEADD(DATE,1,Table.Date)
WHERE PrevDay.Customer is not NULL 
AND NextDay.Customer is not null

Answer 2

Assuming that the data type of the column Date is DATE you can use a self join and aggregation:

SELECT DISTINCT t1.Name
FROM tablename t1 INNER JOIN tablename t2
ON t2.Name = t1.Name AND ABS(DATEDIFF(t1.Date, t2.Date)) = 1
GROUP BY t1.Name, t1.Date
HAVING COUNT(DISTINCT t2.Date) = 2;

Or, a more scalable solution:

SELECT DISTINCT t1.Name
FROM tablename t1 INNER JOIN tablename t2
ON t2.Name = t1.Name AND t2.Date BETWEEN t1.Date AND t1.Date + INTERVAL 2 DAY
GROUP BY t1.Name, t1.Date
HAVING COUNT(DISTINCT t2.Date) = 3;

You can remove DISTINCT from COUNT(DISTINCT t2.Date) if the combination of Name and Date is unique in the table.

See the demo .