Oracle - Loop through a list of columns - oracle

Question

I have a base SQL query that I'm hoping to turn into a dynamic cursor.
I have a list of columns that I am checking to see if the values have changed since previous run, columns that I am checking include: Income, Ethnicity, etc.
The output of the before-and-after values need to be stored in a temp or permanent table for further investigation - such as source of the value change etc...
Because the list of the columns is more than 600+, I don't think I want to compile the base SQL 600 times..
Is there a better way to write out a dynamic SQL cursor to accomplish this task?
Thanks!
---base sql
SELECT a.*,
'Last_name' AS "field_name",
b.LAST_name AS last_name_updated
from
(SELECT person_id, last_name
FROM person
WHERE batch_id = (select max(batch_id) from person)
) a
FULL OUTER JOIN
(SELECT person_id, last_name
FROM person
WHERE batch_id = (select max(batch_id) - 1 from person)
) b
ON a.person_id = b.person_id
WHERE nvl(a.last_name,0) <> nvl(b.last_nm,0)
UNION
SELECT a.*,
'Income',
b.income AS income_updated
from
(SELECT person_id, income
FROM person
WHERE batch_id = (select max(batch_id) from person)
) a
FULL OUTER JOIN
(SELECT person_id, income
FROM person
WHERE batch_id = (select max(batch_id) - 1 from person)
) b
ON a.person_id = b.person_id
WHERE nvl(a.income,0) <> nvl(b.income,0)
---desired output
person_id || field_name || previous_value || updated_value
8783 || income || 95000 || 98000
235731 || last_name || Dawson || Dawson Jr.

Answer 1

Here is something to get you started. Rather than generate one enormous query with 600 unions, it generates 600 queries and runs them sequentially. You would need to add code to save the results from each iteration, perhaps into another table:
declare
l_sql long;
l_default varchar2(10);
l_max_batch_id number;
rc sys_refcursor;
begin
select max(batch_id)
into l_max_batch_id
from person;
for r in (select column_name, data_type
from user_tab_columns
where table_name = 'PERSON'
and column_name not in ('PERSON_ID') -- Exclude any other columns you don't want to compare
)
loop
l_sql := q'[SELECT a.person_id,
a.col AS new_value
'#COL#' AS column_name,
b.#COL# AS old_value
from
(SELECT person_id, #COL#
FROM person
WHERE batch_id = #MAXBATCH#
) a
FULL OUTER JOIN
(SELECT person_id, #COL#
FROM person
WHERE batch_id = #MAXBATCH#-1
) b
ON a.person_id = b.person_id
WHERE nvl(a.#COL#,#DEFAULT#) <> nvl(b.#COL#,#DEFAULT#)]';
l_sql := replace (l_sql, '#COL#', r.column_name);
l_sql := replace (l_sql, '#MAXBATCH#', l_max_batch_id);
l_default := case r.data_type
when 'NUMBER' then '0'
when 'DATE' then q'[DATE '4000-31-12']'
else q'['~~~']'
end;
l_sql := replace (l_sql, '#DEFAULT#', l_default);
open rc for l_sql;
-- Now fetch all the data and e.g. write to a table...
end loop;
end;