Selecting the latest record within a table - sql

Question

I have ant an Oracle v11 database, and whilst I do not have the schema definition of the tables, I have illustrated what I am trying to achieve below.
This is what the table looks like
I am trying to transform the data by selecting only the latest rows, the table keeps an history of changes, I am not interested in the changes only the latest value for every present issue
This is what I have so far.
select issueno,
case (when fieldname = 'name' then string_value end) name,
case (when fieldname = 'point' then string_value end) point
from issues
where issueno = 1234
The issue with the query above is that it returns 4 rows, I would like to return only a single row.

Answer 1

You can get the latest date by using LAST ORDER BY clause within the MAX() KEEP (..) values for transition_date(or load_date column, depending on which you mean replace within the query) such as
WITH i AS
(
SELECT CASE WHEN fieldname = 'name' THEN
MAX(string_value) KEEP (DENSE_RANK LAST ORDER BY transition_date)
OVER (PARTITION BY issue_no, fieldname)
END AS name,
CASE WHEN fieldname = 'point' THEN
MAX(string_value) KEEP (DENSE_RANK LAST ORDER BY transition_date)
OVER (PARTITION BY issue_no, fieldname)
END AS point
FROM issues
)
SELECT MAX(name) AS name, MAX(point) AS point
FROM i
But, if ties(equal values) occur for the related date values, then consider using DENSE_RANK() function in order to compute the values returning equal to 1 along with ROW_NUMBER() to be able to use with the JOIN clause in the main query such as
WITH i AS
(
SELECT i.*,
DENSE_RANK() OVER ( PARTITION BY issue_no, fieldname
ORDER BY transition_date DESC) AS dr,
ROW_NUMBER() OVER ( PARTITION BY issue_no, fieldname
ORDER BY transition_date DESC) AS rn
FROM issues i
)
SELECT i1.string_value AS name, i2.string_value AS point
FROM ( SELECT string_value, rn FROM i WHERE dr = 1 AND fieldname = 'name' ) i1
FULL JOIN ( SELECT string_value, rn FROM i WHERE dr = 1 AND fieldname = 'point' ) i2
ON i2.rn = i1.rn
Demo

Answer 2

Assuming that you want to have the latest record by the column load_date
select issueno,
case (when fieldname = 'name' then string_value end) name,
case (when fieldname = 'point' then string_value end) point
from issues
where issueno = 1234 and
(fieldname , load_date) in (select fieldname ,max(load_date) from issues where issueno=1234 group by fieldname)

Answer 3

I would use a subquery + window function to achieve what you asked for (assuming you use are basing load_date to determine the latest record)
select issueno,
case (when fieldname = 'name' then string_value end) name,
case (when fieldname = 'point' then string_value end) point
from
(
SELECT name, point, ROW_NUMBER() OVER(PARTITION BY ISSUENO, FIELDNAME ORDER BY LOAD_DATE DESC) RN
FROM issues
)
where issueno = 1234
AND RN = 1
The syntax ROW_NUMBER() OVER ([query_partition_clause] order_by_clause) is actually a window function that assign a ranking to each rows governed by how you declare the rule in [query_partition_clause] order_by_clause

Answer 4

See whether something like this helps; read comments within code.
SQL> with issues (issueno, fieldname, string_value,
2 transition_date, transition_id, load_date)
3 as
4 -- sample data; you have it in a table, don't type that
5 (select 1234, 'name', null , date '2021-01-01', 1, date '2021-01-02' from dual union all
6 select 1234, 'name', 'Tom', date '2021-02-11', 2, date '2021-02-12' from dual union all
7 select 1234, 'point', '0' , date '2021-02-04', 3, date '2021-02-05' from dual union all
8 select 1234, 'point', '5' , date '2021-02-10', 5, date '2021-02-11' from dual
9 ),
10 -- query you need begins here
11 temp as
12 -- rank values partitioned by ISSUENO and FIELDNAME, sorted by TRANSITION_ID
13 (select issueno, fieldname, string_value,
14 row_number() over (partition by issueno, fieldname
15 order by transition_id desc) rn
16 from issues
17 )
18 select issueno,
19 max(case when fieldname = 'name' then string_value end) name,
20 max(case when fieldname = 'point' then string_value end) point
21 from temp
22 where rn = 1
23 group by issueno;
ISSUENO NAME POINT
---------- ---------- ----------
1234 Tom 5
SQL>