min and max with and without windowing function - mysql

Question

create table dt
(
id varchar(20),
user_id int,
name varchar(20),
td DATE,
amount float
);
INSERT INTO dt VALUES('blah',1, 'Rodeo', '2018-01-20', 10.12);
INSERT INTO dt VALUES('blahblah',1, 'Rodeo', '2019-01-01', 40.44);
INSERT INTO dt VALUES('sas',2, 'Janice', '2018-02-05', 18.18);
INSERT INTO dt VALUES('dsdcd',3, 'Sam', '2019-01-26', 16.13);
INSERT INTO dt VALUES('sdc',2, 'Janice', '2018-02-01', 12.19);
INSERT INTO dt VALUES('scsc',2, 'Janice', '2017-12-06', 5.10);
+----------+---------+--------+------------+--------+
| id | user_id | name | td | amount |
+----------+---------+--------+------------+--------+
| blah | 1 | Rodeo | 2018-01-20 | 10.12 |
| blahblah | 1 | Rodeo | 2019-01-01 | 40.44 |
| sas | 2 | Janice | 2018-02-05 | 18.18 |
| dsdcd | 3 | Sam | 2019-01-26 | 16.13 |
| sdc | 2 | Janice | 2018-02-01 | 12.19 |
| scsc | 2 | Janice | 2017-12-06 | 5.1 |
+----------+---------+--------+------------+--------+
For the above table how i can get this output. I can achieve this by windowing function but not sure how to do this by correlated subquery. Appreciate any help!
Output
Basically difference of users first transaction amount from their latest transaction amount. If the user has only one transaction then the difference is 0
User_id name amount
1 Rodeo 30.32 [40.44(latest trans) - 10.12 (min trans)]
3 Sam 0
2 Janice 13.08 [18.18 (latest trans) - 5.1 (min trans)]

Answer 1

With 2 subqueries to get the latest and earliest amounts:
select distinct t.user_id, t.name,
(select amount from dt
where user_id = t.user_id
order by td desc limit 1
)
-
(select amount from dt
where user_id = t.user_id
order by td limit 1
) amount
from dt t
See the demo.
Or:
select t.user_id, t.name,
max(t.latest * t.amount) - max(t.earliest * t.amount) amount
from (
select d.user_id, d.name, d.amount,
d.td = g.earliestdate earliest, d.td = g.latestdate latest
from dt d inner join (
select user_id, min(td) earliestdate, max(td) latestdate
from dt
group by user_id
) g on d.user_id = g.user_id and d.td in (earliestdate, latestdate)
) t
group by t.user_id, t.name
See the demo.
Results:
| user_id | name | amount |
| ------- | ------ | ------ |
| 1 | Rodeo | 30.32 |
| 2 | Janice | 13.08 |
| 3 | Sam | 0 |

Answer 2

This is similar to SQL select only rows with max value on a column, but you need to do it twice: once for the earliest row, again for the latest row.
SELECT t1.user_id, t1.name, t1.amount - t2.amount ASA amount
FROM (
SELECT dt1.user_id, dt1.name, dt1.amount
FROM dt AS dt1
JOIN (
SELECT user_id, name, MAX(td) AS maxdate
FROM dt
GROUP BY user_id, name) AS dt2
ON dt1.user_id = dt2.user_id AND dt1.name = dt2.name AND dt1.td = dt2.maxdate
) AS t1
JOIN (
SELECT dt1.user_id, dt1.name, dt1.amount
FROM dt AS dt1
JOIN (
SELECT user_id, name, MIN(td) AS mindate
FROM dt
GROUP BY user_id, name) AS dt2
ON dt1.user_id = dt2.user_id AND dt1.name = dt2.name AND dt1.td = dt2.mindate
) AS t2
ON t1.user_id = t2.user_id AND t1.name = t2.name

Answer 3

Approach using Correlated Subquery:
Query
SELECT user_id,
name,
Round(Coalesce ((SELECT t1.amount
FROM dt t1
WHERE t1.user_id = dt.user_id
ORDER BY t1.td DESC
LIMIT 1) - (SELECT t2.amount
FROM dt t2
WHERE t2.user_id = dt.user_id
ORDER BY t2.td ASC
LIMIT 1), 0), 2) AS amount
FROM dt
GROUP BY user_id,
name;
| user_id | name | amount |
| ------- | ------ | ------ |
| 1 | Rodeo | 30.32 |
| 2 | Janice | 13.08 |
| 3 | Sam | 0 |
View on DB Fiddle

Answer 4

You can try this as well
Select t3.user_id, t3.name, max(t3.new_amount) FROM (
Select t1.user_id, t2.name, (t1.amount - t2.amount) as new_amount
FROM dt t1
INNER JOIN dt t2
ON t1.user_id=t2.user_id
Order by t1.user_id ASC, t1.td DESC, t2.user_id ASC, t2.td ASC
) as t3
group by t3.user_id,t3.name;
Demo