Comparing column by column between two rows in Oracle DB - sql

Question

I need to write a query to compare column by column (ie: find differences) between two rows in the database. For example:
row1: 10 40 sometext 24
row2: 10 25 sometext 24
After the query executed, it should shows only the fields that have difference (ie: the second field)
Here's what I have done so far:
select table1.column1, table1.column2, table1.column3, table1.column4
from table1
where somefield in (field1, field2);
The above query will show me two rows one above another like this:
10 40 sometext 24
10 25 sometext 24
Then I have to manually do the comparison and it takes a lot of time b/c the row contains a lot of column.
So again my question is: How can I write a query that will show me only the columns that have differences??
Thanks

Answer 1

Use UNPIVOT clause (see http://www.oracle-developer.net/display.php?id=506) to turn columns into rows, then filter out the same rows (using GROUP BY HAVING COUNT and finally use PIVOT to get rows with different columns only.

Answer 2

To do this easily you need to query the metadata for the table to get each row. You can use the following code as a script.
Replace the define table_name with your table name and define yes_drop_it = NO. Put your raw WHERE syntax into the where_clause. The comparison logic always compares the first two rows returned for the where clause.
whenever sqlerror exit failure rollback;
set linesize 150
define test_tab_name = tst_cf_cols
define yes_drop_it = YES
define order_by = 1, 2
define where_clause = 1 = 1
define tab_owner = user
<<clearfirst>> begin
for clearout in (
select 'drop table ' || table_name as cmd
from all_tables
where owner = &&tab_owner and table_name = upper('&&test_tab_name')
and '&&yes_drop_it' = 'YES'
) loop
execute immediate clearout.cmd;
execute immediate '
create table &&test_tab_name as
select 10 as column1, 40 as column2, ''sometext'' as column3, 24 as column4 from dual
union all
select 10 as column1, 25 as column2, ''sometext'' as column3, 24 as column4 from dual
';
end loop;
end;
/
column cfsynt format a4000 word_wrap new_value comparison_syntax
with parms as (select 'parmquery' as cte_name, 'row_a' as corr_name_1, 'row_b' as corr_name_2 from dual)
select
'select * from (select ' || LISTAGG(cfcol || ' AS cf_' || trim (to_char (column_id, '000')) || '_' || column_name
, chr(13) || ', ') WITHIN GROUP (order by column_id)
|| chr(13) || ' from (select * from parmquery where row_number = 1) ' || corr_name_1
|| chr(13) || ', (select * from parmquery where row_number = 2) ' || corr_name_2
|| chr(13) || ') where ''DIFFERENT'' IN (' || LISTAGG ('cf_' || trim (to_char (column_id, '000')) || '_' || column_name, chr(13) || ', ') within group (order by column_id) || ')'
as cfsynt
from parms, (
select
'decode (' || corr_name_1 || '.' || column_name || ', ' || corr_name_2
|| '.' || column_name || ', ''SAME'', ''DIFFERENT'')'
as cfcol,
column_name,
column_id
from
parms,
all_tab_columns
where
owner = &&tab_owner and table_name = upper ('&&test_tab_name')
);
with parmquery as (select rownum as row_number, vals.* from (
select * from &&test_tab_name
where &&where_clause
order by &&order_by
) vals
) &&comparison_syntax
;