MySQL - Date Difference and Flags - mysql

Question

I am very new to MySQL and currently working on a table with three columns: trx_id, user_id, last_activity. (Churn Analysis)
tbl_activity:
The table capture activity of users. I am finding it difficulty in performing two tasks.
1) I would like to see two new columns through SQL query
date difference between subsequent transactions.
flag based on condition > 30 days.
Desired table:
2) One of the objectives of this study is to identify when (date) a customer churned. Ideally in my case it would be the 31st day since last activity. Any way to arrive at this date?
I am new to SQL learning and finding it difficult to address SQL queries for the above tasks.

Answer 1

Try this:
For SQL Server:
CREATE TABLE #tbl_activity(Trx_ID INT, User_Id INT, Last_Activity DATETIME)
INSERT INTO #tbl_activity VALUES(1,1100,'2015-06-08')
INSERT INTO #tbl_activity VALUES(2,1100,'2015-06-10')
INSERT INTO #tbl_activity VALUES(3,1100,'2015-06-10')
INSERT INTO #tbl_activity VALUES(4,1100,'2015-06-12')
INSERT INTO #tbl_activity VALUES(5,1100,'2015-06-13')
INSERT INTO #tbl_activity VALUES(6,1100,'2015-06-14')
INSERT INTO #tbl_activity VALUES(7,1100,'2015-09-25')
SELECT T1.Trx_ID, T1.User_Id, T1.Last_Activity
,DATEDIFF(DAY, T1.Last_Activity, T2.Last_Activity) days_Diff
,CASE WHEN DATEDIFF(DAY, T1.Last_Activity, T2.Last_Activity) >30 THEN 1 ELSE 0 END Flag
FROM #tbl_activity T1
LEFT JOIN #tbl_activity T2 ON T1.Trx_ID = T2.Trx_ID-1
DROP TABLE #tbl_activity
For MySQL:
CREATE TABLE tbl_activity(Trx_ID INT, User_Id INT, Last_Activity DATETIME)
INSERT INTO tbl_activity VALUES(1,1100,'2015-06-08')
INSERT INTO tbl_activity VALUES(2,1100,'2015-06-10')
INSERT INTO tbl_activity VALUES(3,1100,'2015-06-10')
INSERT INTO tbl_activity VALUES(4,1100,'2015-06-12')
INSERT INTO tbl_activity VALUES(5,1100,'2015-06-13')
INSERT INTO tbl_activity VALUES(6,1100,'2015-06-14')
INSERT INTO tbl_activity VALUES(7,1100,'2015-09-25')
SELECT T1.Trx_ID, T1.User_Id, T1.Last_Activity
,DATEDIFF(T2.Last_Activity, T1.Last_Activity) days_Diff
,CASE WHEN DATEDIFF(T2.Last_Activity, T1.Last_Activity) >30 THEN 1 ELSE 0 END Flag
FROM tbl_activity T1
LEFT JOIN tbl_activity T2 ON T1.Trx_ID = T2.Trx_ID-1
DROP TABLE tbl_activity
Try this in #SQL Fiddle
Output:
Trx_ID User_Id Last_Activity days_Diff Flag
1 1100 2015-06-08 00:00:00.000 2 0
2 1100 2015-06-10 00:00:00.000 0 0
3 1100 2015-06-10 00:00:00.000 2 0
4 1100 2015-06-12 00:00:00.000 1 0
5 1100 2015-06-13 00:00:00.000 1 0
6 1100 2015-06-14 00:00:00.000 103 1
7 1100 2015-09-25 00:00:00.000 NULL 0