Create a new column of value based on another column - sql

Question

I am new to SQL, and am asked to create two new columns of value based on another column in Oracle Sql.
Here is how data looks like:Under each ID, there is also an IDseq representing a sub-segment in this ID, each with a Start and End place.
SQL needs to help me find the smallest IDseq under each ID, then find the corresponding start place. Similarly, find the largest IDseq under each ID, then find the corresponding end place. Each unique ID would have only one origin and one destination, which will be shown in the two new columns. I'd like to create two new columns (see below) - Origin and Dest to show the origin and destination place for each ID.
Really appreciate your help.

Answer 1

You can use a CASE statement, such as:
select
a.idseq, a.id, a.start, a.end,
case
when a.id = 'ABC' then 'X'
when a.id = 'BCD' then 'Q'
end as origin,
case
when a.id = 'ABC' then 'G'
when a.id = 'BCD' then 'Z'
end as dest
from
yourtablename a

Answer 2

I wrote this before seeing the Oracle tag. MySQL has derived temp table issues, maybe you can avoid the extras in Oracle?
CREATE TEMPORARY TABLE tmp_sequence (
IDSeq INT NOT NULL AUTO_INCREMENT, range_id VARCHAR(3), range_start CHAR(1), range_end CHAR(1), origin CHAR(1), destination CHAR(1), PRIMARY KEY (IDSeq)
);
INSERT INTO tmp_sequence (range_id, range_start, range_end)
VALUES ('ABC', 'X', 'Y'), ('ABC', 'Y', 'H'), ('ABC', 'H','L'), ('ABC','L', 'G'),
('BCD','Q','D'), ('BCD','D','H'),('BCD','H','Z');
CREATE TEMPORARY TABLE tmp_min AS
SELECT MIN(IDSeq) min_id, range_id
FROM tmp_sequence
GROUP BY range_id;
CREATE TEMPORARY TABLE tmp_start AS
SELECT s.min_id, s.range_id, t.range_start
FROM tmp_sequence t
JOIN tmp_min s ON t.IDSeq = s.min_id
AND t.range_id = s.range_id;
UPDATE tmp_sequence t
JOIN tmp_start s ON t.range_id = s.range_id
SET origin = s.range_start;
CREATE TEMPORARY TABLE tmp_max AS
SELECT MAX(IDSeq) max_id, range_id
FROM tmp_sequence
GROUP BY range_id;
CREATE TEMPORARY TABLE tmp_end AS
SELECT s.max_id, s.range_id, t.range_end
FROM tmp_sequence t
JOIN tmp_max s ON t.IDSeq = s.max_id
AND t.range_id = s.range_id;
UPDATE tmp_sequence t
JOIN tmp_end s ON t.range_id = s.range_id
SET destination = s.range_end;
DROP TEMPORARY TABLE tmp_sequence;
DROP TEMPORARY TABLE tmp_min;
DROP TEMPORARY TABLE tmp_start;
DROP TEMPORARY TABLE tmp_end;