I plan to replace each text file into staging table, Create a trigger
on the staging table to "MERGE" the data onto a final table. I have
had to do it this way as sqlldr will not alllow merge.

I've been trying to get the merge working on it's own before inclusion
in a trigger but am getting ORA-00904 - Invalid Identifier. I have
checked and re-checked and cannot spot the error. Any clues anyone?

MERGE INTO "LOAD_TEST_T"
USING (SELECT * from "LOAD_TEST_IN")
ON ("LOAD_TEST_T"."PZ"="LOAD_TEST_IN"."PZ")
WHEN MATCHED THEN
UPDATE
        SET "LOAD_TEST_T"."TEXT"="LOAD_TEST_IN"."TEXT"
WHEN NOT MATCHED THEN
INSERT
        ("LOAD_TEST_T"."PZ", "LOAD_TEST_T"."TEXT")
VALUES
        ("LOAD_TEST_IN"."PZ", "LOAD_TEST_IN"."TEXT");

I'll be extremely embarrassed if it's a typo.........

MERGE INTO "LOAD_TEST_T"
USING (SELECT * from "LOAD_TEST_IN") LOAD_TEST_IN
ON ("LOAD_TEST_T"."PZ"="LOAD_TEST_IN"."PZ")
WHEN MATCHED THEN
UPDATE
         SET "LOAD_TEST_T"."TEXT"="LOAD_TEST_IN"."TEXT"
WHEN NOT MATCHED THEN
INSERT
         ("LOAD_TEST_T"."PZ", "LOAD_TEST_T"."TEXT")
VALUES
         ("LOAD_TEST_IN"."PZ", "LOAD_TEST_IN"."TEXT");

or even more simply:

MERGE INTO "LOAD_TEST_T"
USING LOAD_TEST_IN
ON ("LOAD_TEST_T"."PZ"="LOAD_TEST_IN"."PZ")
WHEN MATCHED THEN
UPDATE
         SET "LOAD_TEST_T"."TEXT"="LOAD_TEST_IN"."TEXT"
WHEN NOT MATCHED THEN
INSERT
         ("LOAD_TEST_T"."PZ", "LOAD_TEST_T"."TEXT")
VALUES
         ("LOAD_TEST_IN"."PZ", "LOAD_TEST_IN"."TEXT");

Best regards

Maxim