Comparing Dates by Fixed Level of Detail in mySQL

Question

Good Morning,

I'm trying to create a mySQL query with the following output:

In order to get the 60_days_since_seen, I need to compare the reference_date for the current row to the next most recent reference_date relative to the unique_identifier and determine if that reference_date is older than 60 days from the reference_date from that row.

Ex: unique_identifier = 123456789

id = 1: Since there is no date before this instance, the 60_days_since_seen is TRUE (or 1).

id = 2: Since the date of the reference_date occurrence prior to this id relative to the unique_identifier is less than 60 days since this row's reference_date, the 60_days_since_seen is FALSE (or 0).

id = 3: Since the date of the reference_date occurrence prior to this id relative to the unique_identifier is greater than 60 days since this row's reference_date, the 60_days_since_seen is TRUE (or 1).

id = 4: Since there is no date before this instance, the 60_days_since_seen is TRUE (or 1).

id = 5: Since the date of the reference_date occurrence prior to this id relative to the unique_identifier is less than 60 days since this row's reference_date, the 60_days_since_seen is FALSE (or 0).

Answer 1

The first query works also with mysql 5.x.

The second uses window functions that are only supported in mysql 8

CREATE TABLE datetable (
  `Id` INTEGER,
  `unique_identifier` INTEGER,
  `reference_date` Date
);

INSERT INTO datetable
  (`Id`, `unique_identifier`, `reference_date`)
VALUES
  ('1', '123456789', '2020-01-05'),
  ('2', '123456789', '2020-02-20'),
  ('3', '123456789', '2020-06-29'),
  ('4', '987654321', '2020-02-21'),
  ('5', '987654321', '2020-03-30');

SELECT
`Id`, `reference_date`
,IF(@unique_identifier = `unique_identifier`,IF(DATEDIFF(`reference_date`,@date) > 60,1,0),1) 60_days_since_seen
,@unique_identifier := `unique_identifier` as 'unique_identifier'
,@date :=`reference_date` 'reference_date'
FROM
(SELECT * FROM datetable ORDER BY unique_identifier,reference_date) t1
,(SELECT @unique_identifier := 0) a,(SELECT @date := NOW()) b

Id | reference_date | 60_days_since_seen | unique_identifier | reference_date
-: | :------------- | -----------------: | ----------------: | :-------------
 1 | 2020-01-05     |                  1 |         123456789 | 2020-01-05    
 2 | 2020-02-20     |                  0 |         123456789 | 2020-02-20    
 3 | 2020-06-29     |                  1 |         123456789 | 2020-06-29    
 4 | 2020-02-21     |                  1 |         987654321 | 2020-02-21    
 5 | 2020-03-30     |                  0 |         987654321 | 2020-03-30    

SELECT
`Id`, `unique_identifier`, `reference_date`,
   IF(DATEDIFF(reference_date , LAG(reference_date) OVER (
        PARTITION BY unique_identifier
        ORDER BY reference_date ))> 60 OR LAG(reference_date) OVER (
        PARTITION BY unique_identifier
        ORDER BY reference_date ) is NULL,1,0) 60_days_since_seen
FROM datetable

Id | unique_identifier | reference_date | 60_days_since_seen
-: | ----------------: | :------------- | -----------------:
 1 |         123456789 | 2020-01-05     |                  1
 2 |         123456789 | 2020-02-20     |                  0
 3 |         123456789 | 2020-06-29     |                  1
 4 |         987654321 | 2020-02-21     |                  1
 5 |         987654321 | 2020-03-30     |                  0

db<>fiddle here