How to Update the Following Table with MERGE in Oracle? - sql

Question

I have the following data set (Oracle 12):
Table X
+---------+--------+---------------+--------+
| COLN | COLM | COLK | COLP |
+---------+--------+---------------+--------+
| 1 | 500 | K1 | 777 |
+---------+--------+---------------+--------+
Table A
+---------+--------+---------------+--------+
| COL1 | COL2 | COL3 | COL4 |
+---------+--------+---------------+--------+
| 1 | K1 | 500 | B |
| 1 | K2 | 500 | NULL |
+---------+--------+---------------+--------+
Table B
+---------+--------+---------+
| COLZ | COLX | COLW |
+---------+--------+---------+
| 1 | K1 | 777 |
| 1 | K2 | 678 |
+---------+--------+---------+
The three tables have the following commonality:
X.COLN = A.COL1 = B.COLZ
X.COLk = A.COL2 = B.COLX
X.COLM = A.COL3
I need to write a query which retrieves values for the following columns in one query:
X.COLK, X.COLP, B.COLX, B.COLW
The ultimate goal is, if the following conditions are met:
If there more than one record in Table A where A.COL1's and A.COL3's are matching (and there is a corresponding record in Table X)
And one of the rows is not null, e.g. A.COL4 = B, and another one is NULL
I update Table X to replace X.COLK, X.COLP (K1 and 777) in my MERGE statement with values in Table B (B.COLX, B.COLW -- K2 and 678).
Is this possible?
MERGE INTO X FX
USING (
SELECT COLX ONGOING_X, COLW ONGOING_W
FROM B
WHERE (COLZ, COLX) IN
(SELECT COL1, COL2
FROM A
WHERE COL3 = ?
AND COL1 = ?
AND COL4 IS NULL)
) NEW_B
ON (FX.COLk = ?
AND FX.COLP = ?)
WHEN MATCHED THEN
UPDATE SET
FX.COLk = NEW_B.ONGOING_X,
FX.FOLP = NEW_B.ONGOING_W;

Answer 1

You may do a MERGE using ROWID.
MERGE INTO x tgt USING (
WITH c AS (
SELECT col1,
col3,
MAX(
CASE
WHEN col4 IS NULL THEN col2
END
) AS col2 --Ongoing col2 as indicated from col4
FROM a
GROUP BY col1,
col3
HAVING COUNT(
CASE
WHEN col4 IS NULL THEN 1
END
) = 1 AND COUNT(col4) = 1 --Contains one and exactly one NULL and one NON NULL
) SELECT x.rowid AS rid,
b.*
FROM x
JOIN c ON c.col1 = x.coln AND c.col3 = x.colm
JOIN b ON b.colz = c.col1 AND b.colx = c.col2 --Join with ongoing value from c( a.k.a table A )
)
src ON ( tgt.rowid = src.rid ) --ROWID match
WHEN MATCHED THEN UPDATE SET tgt.colk = src.colx,
tgt.colp = src.colw;
Demo