How to get last modified row with condition - mysql

Question

I have below mentioned tables:
Table1:
ID Unique_Key Date MapId
II-10 RTE-011 2018-04-07 15:18:25 er-12-tt
II-11 RTE-011 2018-05-17 11:44:47 er-13-td
II-12 RTE-011 2018-06-12 13:22:29 ee-13-rt
II-13 RTE-012 2018-04-07 19:17:14 eg-15-st
II-14 RTE-012 2018-04-07 21:22:37 hr-15-yt
II-15 RTE-013 2018-07-07 20:27:38 tr-16-yt
II-15 RTE-013 2018-08-07 14:18:33 tr-16-yt
Table2:
Id Status
er-12-tt Open
er-13-td Closed
er-13-rt Closed
eg-15-st Closed
hr-15-yt Pending
tr-16-yt Open
tr-16-yt Pending
By using above mentioned both the tables, I want to fetch latest row of only those records which has status as Closed.
We need to exclude those Unique_Key against which any value is not equlal to Closed
Required Output would be:
ID Unique_Key Date MapId Id Status
II-12 RTE-011 2018-06-12 13:22:29 ee-13-rt er-13-rt Closed
II-13 RTE-012 2018-04-07 19:17:14 eg-15-st eg-15-st Closed

Answer 1

Firstly, in a subquery, we determine the maximum date for a group of Unique_Key. We filter out those Unique_Key values which has atleast one row with Status = Closed, using HAVING SUM(t2.Status = Closed) > 0
The result set of this sub-query is then utilized as a Derived Table. It is then joined back to Table1 and Table2, and we filter out those cases where maximum status is Closed, using WHERE t22.Status = 'Closed'
Try:
SELECT t11.ID,
t11.Unique_Key,
t11.Date,
t11.MapId,
t22.Id,
t22.Status
FROM Table1 AS t11
JOIN Table2 AS t22 ON t22.Id = t11.MapId
JOIN (
SELECT t1.Unique_Key,
MAX(t1.Date) AS max_Date
FROM Table1 AS t1
JOIN Table2 AS t2 ON t2.Id = t1.MapId
GROUP BY t1.Unique_Key
HAVING SUM(t2.Status = Closed) > 0
) AS dt ON dt.Unique_Key = t11.Unique_Key AND
dt.max_Date = t11.Date
WHERE t22.Status = 'Closed'

Answer 2

We can take a common approach here, and join to a subquery to do the filtering:
SELECT
t1.ID, t1.Unique_Key, t1.Date, t1.MapId, t2.Id, t2.Status
FROM Table1 t1
INNER JOIN Table2 t2
ON t1.MapId = t2.Id
INNER JOIN
(
SELECT t1.Unique_Key, MAX(t1.Date) AS max_date
FROM Table1 t1
INNER JOIN Table2 t2
ON t1.MapId = t2.Id
WHERE t2.Status = 'Closed'
GROUP BY t1.Unique_Key
) t3
ON t1.Unique_Key = t3.Unique_Key AND t1.Date = t3.max_date;
Demo
The join to the subquery aliased as t3 filters off all records for each unique key except for the most recent one which has a closed status.
For posterity's sake, there is another approach to this question using analytic functions. Given that MySQL 8+ will soon be the standard, it makes sense to consider this option as well:
SELECT
ID_t1, Unique_Key, Date, MapId, ID_t2, Status
FROM
(
SELECT t1.ID AS ID_t1, t1.Unique_Key, t1.Date, t1.MapId, t2.Id AS ID_t2,
t2.Status,
ROW_NUMBER() OVER (PARTITION BY t1.Unique_Key ORDER BY t1.Date DESC) rn
FROM Table1 t1
INNER JOIN Table2 t2
ON t1.MapId = t2.Id
WHERE t2.Status = 'Closed'
) t
WHERE rn = 1;
Demo