How to compare datetime and get first and last date MySQL - mysql

Question

I have below mentioned tables: MySQL Version - 5.7.25
Table1:
ID ref
T-1 abc-1-x
T-2 abc-2-x
T-3 abc-3-x
T-4 abc-4-x
T-5 abc-5-x
Table2
ref_id value date
abc-1-x 250 2019-12-10 14:16:19
abc-2-x 500 2019-12-11 17:21:05
abc-3-x 100 2019-12-12 18:11:01
abc-4-x 150 2019-12-13 05:04:11
abc-5-x 120 2019-12-14 12:10:09
Table3
ID seq date2
T-1 1 2019-12-10 14:05:04
T-1 2 2019-12-10 21:17:01
T-1 3 2019-12-11 13:12:12
T-2 1 2019-12-11 14:13:46
T-2 2 2019-12-12 14:05:04
T-3 1 2019-12-12 14:05:04
T-3 2 2019-12-12 17:15:14
T-3 3 2019-12-13 10:09:08
T-3 4 2019-12-14 12:18:14
T-4 1 2019-12-13 01:01:04
T-4 2 2019-12-13 03:03:01
T-5 1 2019-12-15 14:05:04
By utilizing the above mentioned three tables, I want to compare the date of Table2 with Table3 against each ID, and fetch the first date and last date from Table3 against each id.
Scenarios:
If any date of Table3 less than against particular id in Table2 show it as Less
If any date of Table3 equal to against particular id in Table2 show it as Same
If any date of Table3 greater than against particular id in Table2 show it as Greater
Required Output:
ID Value date date1 date2 remarks day_diff
T-1 250 2019-12-10 14:16:19 2019-12-10 14:05:04 2019-12-11 13:12:12 Greater 1
T-2 500 2019-12-11 17:21:05 2019-12-11 14:13:46 2019-12-12 14:05:04 Greater 1
T-3 100 2019-12-12 18:11:01 2019-12-12 14:05:04 2019-12-14 12:18:14 Greater 2
T-4 150 2019-12-13 05:04:11 2019-12-13 01:01:04 2019-12-13 03:03:01 Same 0
T-5 120 2019-12-14 12:10:09 2019-12-15 14:05:04 Null Greater 1

Answer 1

You can use a subquery to generate the MAX and MIN dates from Table3 for each entry in Table2 and then generate the Greater/Same/Less values in an outer query:
SELECT *,
CASE WHEN DATE(date2) > DATE(date) OR DATE(date1) > DATE(date) THEN 'Greater'
WHEN DATE(date2) < DATE(date) OR DATE(date1) < DATE(date) THEN 'Less'
ELSE 'Same'
END AS remarks,
DATEDIFF(date2, date) AS day_diff
FROM (
SELECT t3.ID, t2.Value, t2.date, MIN(t3.date2) AS date1, MAX(t3.date2) AS date2
FROM Table1 t1
JOIN Table2 t2 ON t2.ref_id = t1.ref
JOIN Table3 t3 ON t3.ID = t1.ID
GROUP BY t3.ID, t2.Value, t2.date
) g
Output:
ID Value date date1 date2 remarks day_diff
T-1 250 2019-12-10 14:16:19 2019-12-10 14:05:04 2019-12-11 13:12:12 Greater 1
T-2 500 2019-12-11 17:21:05 2019-12-11 14:13:46 2019-12-12 14:05:04 Greater 1
T-3 100 2019-12-12 18:11:01 2019-12-12 14:05:04 2019-12-14 12:18:14 Greater 2
T-4 150 2019-12-13 05:04:11 2019-12-13 01:01:04 2019-12-13 03:03:01 Same 0
T-5 120 2019-12-14 12:10:09 2019-12-15 14:05:04 2019-12-15 14:05:04 Greater 1
Note that if there is only one date for a Table2 value in Table3, this will give the same values for date1 and date2. If you really want NULL for date2 in that case, change the SELECT * in the above query to
SELECT ID, Value, date, date1,
CASE WHEN date1 = date2 THEN NULL ELSE date2 END AS date2,
Demo on dbfiddle