APEX

Hi, @jackbox1098
When querying the dba_tab_cols againt the col_audit_tab only the matching tables are returned. We need to find all tables that do not yet exist in the col_audit_tab and insert them.
To find rows that are in one table but not another, you can use MINUS, NOT EXISTS, NOT IN or outer join.
We have attached some test data.
Post the sample data, the exact results you want from that sample data, and an explanation of how you get those results from that data right in this space. Do not use attachments. Not everyone who wants to help you can or will open attahements.

Hi, @jackbox1098
'COL_A','COL_B','COL_C' is constant?
SELECT
tc.table_name,
MAX(
CASE
WHEN tc.column_name = 'COL_A' THEN
tc.column_name
ELSE
NULL
END
) AS col_a,
MAX(
CASE
WHEN tc.column_name = 'COL_B' THEN
tc.column_name
ELSE
NULL
END
) AS col_b,
MAX(
CASE
WHEN tc.column_name = 'COL_C' THEN
tc.column_name
ELSE
NULL
END
) AS col_c
FROM
user_tab_cols tc
--RIGHT JOIN myuser.col_audit_tab at ON tc.table_name = at.table_name
WHERE
tc.table_name<>'COL_AUDIT_TAB' -- and owner='MYUSER'
and tc.column_name in ('COL_A','COL_B','COL_C')
and not exists (
select 1
from col_audit_tab at
where tc.table_name = at.table_name and (tc.column_name=at.COL_A or tc.column_name=at.COL_B or tc.column_name=at.COL_C)
)
GROUP By
tc.table_name

OP, if I got it right, is looking for both ways changes - additions to audit table and removal of what is no longer valid from audit table. Therefore it should be MERGE into audit table using full outer join between DBA_TAB_COLS and audit table. That is if OP wants to store results in a table. I'd look into creating a view as full outer join between DBA_TAB_COLS and audit table.
SY.

Thanks to all for your feedback!
@stax Thanks for the script. Still not returning the table names that are in the data dictionary, but not in the audit table.
@solomon-yakobson We need to add all table names to the audit table that are in the data dictionary. No deletions, only inserts.
Tables with the mentioned columns above must be saved in the col_audit_tab; i.e.
-> Audit table columns: Table_name col_a col_b col_c
-> Entries: Key_tab col_a col_b col_c
Key_tab2 col_a null col_c

@stax Thanks for the script. Still not returning the table names that are in the data dictionary, but not in the audit table.
I do not understand what is needed, you can example
ps
there is no information about KEY_COL_TAB2.COL_B in col_audit_tab, so the script returned it

Our goal is to query the dba_tab_cols and save all tables in the audit table that have these specific columns. The table names here are only examples.
We can use different table and column names i.e. Labels, Handbooks, Services. ID_CLIENT1, ID_CLIENT2, ID_CLIENT3 to make it clearer.

that have these specific columns
"specific columns" (COL_A,COL_B,COL_C) the constants in script?
example:

1. exist the table DEPT, not present in  in the audit table

OWNER	TABLE_NAME	COLUMN_NAME
STAX	DEPT		DEPTNO
STAX	DEPT		DNAME
STAX	DEPT		LOC

2. exist the table Key_tab2 and present in col_audit_tab (COL_B not in the audit table)
   that should return the script?

The output (COL_AUDIT_TAB) should be like this:
OWNER TABLE_NAME ID_CLIENT1 ID_CLIENT2 ID_CLIENT3
USER1 LABELS ID_CLIENT1 NULL ID_CLIENT3
USER1 SERVICES NULL ID_CLIENT2 NULL
Important is that all tables are saved that have at least 1 of these columns.
Thanks!

@solomon-yakobson Thanks a lot! This should do it. I will test it in our system tomorrow. Feedback to follow.