Select most recent test score on per month basis - sql

Question

I am using Oracle SQL, and I'm trying to perform a historical test score analysis (to visualize test score improvements on per month basis for individuals). Firstly, I have a table that is a list of Users and the respective Months they are active; it looks something like this:
TABLE1
________________________
UserName | ActiveDate
________________________
John Doe, 01-MAY-18
John Doe, 01-APR-18
John Doe, 01-MAR-18
Jane Doe, 01-APR-18
Jane Doe, 01-MAR-18
Jim Doe, 01-MAY-18
On top of that, I have another table that lists Test Scores, which are timestamped (you can retake the test as many times as you want). It looks something like this:
TABLE2
________________________________________
UserName | TestScore | EffectiveDate
________________________________________
John Doe, 87, 07-FEB-18
John Doe, 85, 14-FEB-18
John Doe, 90, 18-FEB-18
John Doe, 92, 02-MAR-18
John Doe, 91, 12-MAR-18
Jane Doe, 70, 01-FEB-18
Jane Doe, 72, 02-FEB-18
Jane Doe, 78, 18-FEB-18
Jane Doe, 77, 06-MAR-18
Jane Doe, 81, 18-MAR-18
Jim Doe, 50, 03-MAR-18
Jim Doe, 48, 23-MAR-18
Jim Doe, 58, 08-APR-18
For every row in the first table (all the UserName | ActiveDate pairings are disctinct), I would like to select the most recent TestScore from Table2 where the EffectiveDate is prior to the ActiveDate
So I'm hoping to get something like this
UserName | ActiveDate | Most recent TestScore prior to ActiveDate
______________________________________
John Doe, 01-MAY-18, 91
John Doe, 01-APR-18, 91
John Doe, 01-MAR-18, 90
Jane Doe, 01-APR-18, 81
Jane Doe, 01-MAR-18, 78
Jim Doe, 01-MAY-18, 58
I've tried to make this work by JOINING Table1 to Table2 on UserName, where EffectiveDate < ActiveDate, but I can't seem to figure out the SQL statement I need to SELECT * from Table2 where EffectiveDate < ActiveDate, but I'm struggling to figure that out on a "per row" basis...
Thanks for any and all advice in advance. This is my first posting to StackOverflow, so I hope I've posed this question correctly!
Edit: Thanks all for the help, I think I have everything I need to proceed with my project now. I'll be sure to make some improvements to my posting next time I ask a question here on SO.

Answer 1

Two solutions that only require a single join:
Oracle Setup:
CREATE TABLE TABLE1 ( UserName, ActiveDate ) AS
SELECT 'John Doe', DATE '2018-05-01' FROM DUAL UNION ALL
SELECT 'John Doe', DATE '2018-04-01' FROM DUAL UNION ALL
SELECT 'John Doe', DATE '2018-03-01' FROM DUAL UNION ALL
SELECT 'Jane Doe', DATE '2018-04-01' FROM DUAL UNION ALL
SELECT 'Jane Doe', DATE '2018-03-01' FROM DUAL UNION ALL
SELECT 'Jim Doe', DATE '2018-05-01' FROM DUAL;
CREATE TABLE TABLE2 ( UserName, TestScore, EffectiveDate ) AS
SELECT 'John Doe', 87, DATE '2018-02-07' FROM DUAL UNION ALL
SELECT 'John Doe', 85, DATE '2018-02-14' FROM DUAL UNION ALL
SELECT 'John Doe', 90, DATE '2018-02-18' FROM DUAL UNION ALL
SELECT 'John Doe', 92, DATE '2018-03-02' FROM DUAL UNION ALL
SELECT 'John Doe', 91, DATE '2018-03-12' FROM DUAL UNION ALL
SELECT 'Jane Doe', 70, DATE '2018-02-01' FROM DUAL UNION ALL
SELECT 'Jane Doe', 72, DATE '2018-02-02' FROM DUAL UNION ALL
SELECT 'Jane Doe', 78, DATE '2018-02-18' FROM DUAL UNION ALL
SELECT 'Jane Doe', 77, DATE '2018-03-06' FROM DUAL UNION ALL
SELECT 'Jane Doe', 81, DATE '2018-03-18' FROM DUAL UNION ALL
SELECT 'Jim Doe', 50, DATE '2018-03-03' FROM DUAL UNION ALL
SELECT 'Jim Doe', 48, DATE '2018-03-23' FROM DUAL UNION ALL
SELECT 'Jim Doe', 58, DATE '2018-04-08' FROM DUAL;
Query 1:
SELECT *
FROM (
SELECT t2.*,
t1.ActiveDate,
ROW_NUMBER() OVER ( PARTITION BY t2.UserName, t1.ActiveDate ORDER BY EffectiveDate DESC ) AS rn
FROM table2 t2
INNER JOIN
table1 t1
ON ( t1.UserName = t2.UserName
AND t2.EffectiveDate < t1.ActiveDate )
) t2
WHERE rn = 1;
Output:
USERNAME TESTSCORE EFFECTIVEDATE ACTIVEDATE RN
---------- ---------- -------------- ---------- ---
Jane Doe 78 18-FEB-18 01-MAR-18 1
Jane Doe 81 18-MAR-18 01-APR-18 1
Jim Doe 58 08-APR-18 01-MAY-18 1
John Doe 90 18-FEB-18 01-MAR-18 1
John Doe 91 12-MAR-18 01-APR-18 1
John Doe 91 12-MAR-18 01-MAY-18 1
Query 2:
SELECT t1.UserName,
t1.ActiveDate,
MAX( TestScore ) KEEP ( DENSE_RANK LAST ORDER BY EffectiveDate ) AS MostRecentTestScore
FROM table2 t2
INNER JOIN
table1 t1
ON ( t1.UserName = t2.UserName
AND t2.EffectiveDate < t1.ActiveDate )
GROUP BY t1.UserName, t1.ActiveDate;
Output:
USERNAME ACTIVEDATE MOSTRECENTTESTSCORE
---------- ---------- -------------------
Jim Doe 01-MAY-18 58
Jane Doe 01-MAR-18 78
Jane Doe 01-APR-18 81
John Doe 01-MAR-18 90
John Doe 01-APR-18 91
John Doe 01-MAY-18 91

Answer 2

If you just want the test score, a correlated subquery might be the simplest approach:
select t1.*,
(select max(t2.score) keep (dense_rank first order by t2.effectivedate desc)
from table2 t2
where t2.effectivedate < t1.activedate
) as most_recent_score
from table1 t1;

Answer 3

Here's one option (you need lines 24 onwards; previous lines are just testing CTEs):
SQL> with table1 (username, activedate) as
2 (select 'jod', date '2018-05-01' from dual union all
3 select 'jod', date '2018-04-01' from dual union all
4 select 'jod', date '2018-03-01' from dual union all
5 select 'jad', date '2018-04-01' from dual union all
6 select 'jad', date '2018-03-01' from dual union all
7 select 'jid', date '2018-05-01' from dual
8 ),
9 table2 (username, testscore, effectivedate) as
10 (select 'jod', 87, date '2018-02-07' from dual union all
11 select 'jod', 85, date '2018-02-14' from dual union all
12 select 'jod', 90, date '2018-02-18' from dual union all
13 select 'jod', 92, date '2018-03-02' from dual union all
14 select 'jod', 91, date '2018-03-12' from dual union all
15 select 'jad', 70, date '2018-02-01' from dual union all
16 select 'jad', 72, date '2018-02-02' from dual union all
17 select 'jad', 78, date '2018-02-18' from dual union all
18 select 'jad', 77, date '2018-03-06' from dual union all
19 select 'jad', 81, date '2018-03-18' from dual union all
20 select 'jid', 50, date '2018-03-03' from dual union all
21 select 'jid', 48, date '2018-03-23' from dual union all
22 select 'jid', 58, date '2018-04-08' from dual
23 )
24 select t1.username, t1.activedate, t2.testscore
25 from table1 t1 join table2 t2 on t1.username = t2.username
26 where t2.effectivedate = (select max(t2a.effectivedate)
27 from table2 t2a
28 where t2a.username = t2.username
29 and t2a.effectivedate < t1.activedate
30 )
31 order by t1.username, t1.activedate desc;
USE ACTIVEDAT TESTSCORE
--- --------- ----------
jad 01-apr-18 81
jad 01-mar-18 78
jid 01-may-18 58
jod 01-may-18 91
jod 01-apr-18 91
jod 01-mar-18 90
6 rows selected.
SQL>