SQL Merge rows instead of UNION ALL - sql

Question

I'm doing a UNION ALL to get the results as shows in the table below. This approach is causing to have unnecessary rows. The three columns DESK, SEGMENT and SUPERVISOR are independent and have no relationship.
Code
SELECT ID, DESK, '' as SEGMENT, '' as SUPERVISOR FROM myTable1
UNION ALL
SELECT ID, '' AS DESK, SEGMENT, '' as SUPERVISOR FROM myTable2
UNION ALL
SELECT ID, '' AS DESK, '' as SEGMENT, SUPERVISOR FROM myTable3
Result:
+------+------------+---------+------------+
| ID | DESK | SEGMENT | SUPERVISOR | TOTAL ENTRIES
+------+------------+---------+------------+
| 4782 | OIL & GAS | | | 23
+------+------------+---------+------------+
| 4782 | AUTOMOTIVE | | | 23
+------+------------+---------+------------+
| 4782 | | GLOBAL | | 23
+------+------------+---------+------------+
| 4782 | | | DANIEL | 23
+------+------------+---------+------------+
| 4782 | | | JAMES | 23
+------+------------+---------+------------+
How can I query to get the below result?
Expected Result:
+------+------------+---------+------------+
| ID | DESK | SEGMENT | SUPERVISOR | TOTAL ENTRIES
+------+------------+---------+------------+
| 4782 | OIL & GAS | GLOBAL | DANIEL | 23
+------+------------+---------+------------+
| 4782 | AUTOMOTIVE | | JAMES | 23
+------+------------+---------+------------+

Answer 1

You can use ROW_NUMBER() analytic function with partitioned by ID column along with FULL OUTER JOIN for those three tables like this :
SELECT NVL(NVL(t2.ID,t3.ID),t1.ID) AS ID, desk, segment, supervisor
FROM ( SELECT t1.*, ROW_NUMBER() OVER (PARTITION BY ID ORDER BY 0) AS rn FROM myTable1 t1 ) t1
FULL JOIN ( SELECT t2.*, ROW_NUMBER() OVER (PARTITION BY ID ORDER BY 0) AS rn FROM myTable2 t2 ) t2
ON t2.ID = t1.ID AND t2.rn = t1.rn
FULL JOIN ( SELECT t3.*, ROW_NUMBER() OVER (PARTITION BY ID ORDER BY 0) AS rn FROM myTable3 t3 ) t3
ON t3.ID = t1.ID AND t3.rn = t1.rn;
ID DESK SEGMENT SUPERVISOR
---- ---------- ------- ----------
4782 AUTOMOTIVE GLOBAL JAMES
4782 OIL & GAS DANIEL
Demo
P.S: I left ORDER BY 0 as ORDER BY option is mandatory for ROW_NUMBER(), you can replace zero with a proper column or identifier for you.

Answer 2

You can try this:
SELECT table1.ID, table1.DESK, table2.SEGMENT, (select SUPERVISOR from (select SUPERVISOR, ROWNUM AS RN FROM table3) WHERE RN = 1) SUPERVISOR
FROM table1 JOIN table2 on table1.ID = table2.ID
WHERE table1.DESK = 'OIL & GAS'
UNION ALL
SELECT table1.ID, table1.DESK, null SEGMENT, (select SUPERVISOR from (select SUPERVISOR, ROWNUM AS RN FROM table3) WHERE RN = 2) SUPERVISOR
FROM table1 JOIN table2 on table1.ID = table2.ID
WHERE table1.DESK = 'AUTOMOTIVE'
https://dbfiddle.uk/?rdbms=oracle_11.2&fiddle=c5594bb1d99579611d2669f6bab675a2

Answer 3

You can try a query like the one below. I don't know where the 23 is coming from so I did not factor it into the query, but if it is a column in one of the three tables, similar logic can be used to add it to the results.
Query
WITH
table1 (id, desk)
AS
(SELECT 4782, 'OIL & GAS' FROM DUAL
UNION ALL
SELECT 4782, 'AUTOMOTIVE' FROM DUAL),
table2 (id, segment) AS (SELECT 4782, 'GLOBAL' FROM DUAL),
table3 (id, supervisor)
AS
(SELECT 4782, 'DANIEL' FROM DUAL
UNION ALL
SELECT 4782, 'JAMES' FROM DUAL)
SELECT *
FROM (SELECT t1.id,
CASE WHEN t1.desk = LAG (t1.desk) OVER (ORDER BY t1.desk) THEN NULL ELSE t1.desk END
AS desk,
CASE
WHEN t2.segment = LAG (t2.segment) OVER (ORDER BY t2.segment) THEN NULL
ELSE t2.segment
END
AS segment,
CASE
WHEN t3.supervisor = LAG (t3.supervisor) OVER (ORDER BY t3.supervisor) THEN NULL
ELSE t3.supervisor
END
AS supervisor
FROM table1 t1, table2 t2, table3 t3
WHERE t1.id = t2.id AND t1.id = t3.id)
WHERE desk IS NOT NULL OR segment IS NOT NULL OR supervisor IS NOT NULL;
Result
ID DESK SEGMENT SUPERVISOR
_______ _____________ __________ _____________
4782 AUTOMOTIVE GLOBAL DANIEL
4782 OIL & GAS JAMES