MERGE UPSERT DOES NOT WORK WHEN NOT MATCHED - sql

Question

ABC_TABLE holds history data based on UPDATED_TS column.
Requirement is to load data from a CSV file and conditions is as below:
Fetch the latest EMPLOYEE_NAME based on UPDATED_TS (query inside USING condition)
In ON condition check, if the EMPLOYEE_NAME in CSV file does not match the EMPLOYEE_NAME fetched in the USING query, a new row should be inserted
If a new TABLE_ID is present in the CSV file and the TABLE_ID does not exist in ABC_TABLE, a new record should be inserted
When executing below query, no rows get inserted for a new TABLE_ID,
MERGE INTO ABC_TABLE T
USING (SELECT EMPLOYEE_NAME
FROM ABC_TABLE
WHERE TABLE_ID = ?
AND UPDATED_TS =
(SELECT MAX(UPDATED_TS) FROM ABC_TABLE WHERE TABLE_ID = ?)) S
ON ((S.EMPLOYEE_NAME IS NULL AND ? IS NULL) OR ? = S.EMPLOYEE_NAME )
WHEN NOT MATCHED THEN
INSERT
/*
insert statement here
*/
Any help would be greatly appreciated.

Answer 1

The merge documentation says:
Use the ON clause to specify the condition upon which the MERGE operation either updates or inserts. For each row in the target table for which the search condition is true, Oracle Database updates the row with corresponding data from the source table. If the condition is not true for any rows, then the database inserts into the target table based on the corresponding source table row.
For both matched and not-matched, there has to be a row in the source table (your S subquery in this case) for anything to happen. If the passed-in values don't exist then your subquery finds no rows, so source table is empty, and thus nothing happens.
You could add an aggregate function call in your subquery so it always finds something, and use that (e.g. a count of found records) to decide if it's matched; something like:
MERGE INTO ABC_TABLE T
USING (SELECT :table_id AS TABLE_ID, :employee_name AS EMPLOYEE_NAME, count(*) AS FOUND
FROM ABC_TABLE
WHERE TABLE_ID = :table_id
AND ((EMPLOYEE_NAME IS NULL AND :employee_name IS NULL)
OR EMPLOYEE_NAME = :employee_name)
AND UPDATED_TS =
(SELECT MAX(UPDATED_TS) FROM ABC_TABLE WHERE TABLE_ID = :table_id)) S
ON (S.FOUND > 0)
WHEN NOT MATCHED THEN
INSERT (table_id, updated_ts, employee_name)
VALUES (S.TABLE_ID, systimestamp, S.EMPLOYEE_NAME)
But as you're only inserting and never updating, why not just use an insert?
INSERT INTO ABC_TABLE T (table_id, updated_ts, employee_name)
SELECT :table_id, systimestamp, :employee_name
FROM DUAL
WHERE NOT EXISTS (
SELECT null
FROM ABC_TABLE T2
WHERE T2.TABLE_ID = :table_id
AND ((T2.EMPLOYEE_NAME IS NULL AND :employee_name IS NULL)
OR T2.EMPLOYEE_NAME = :employee_name)
AND UPDATED_TS =
(SELECT MAX(UPDATED_TS) FROM ABC_TABLE WHERE TABLE_ID = :table_id)
)
I'm not sure you actually want the UPDATED_TS check in either case though.