Oracle Compare 2 equijoined tables - oracle

Question

The concept is that i am trying to compare 2 equijoined tables to see if the whether the other query has the same values or if they exist in the other query.
The way i join the tables is:
"select a.sth, a.sth2, a.st3, b.value for table1 a, table2 b where a.key = b.valkey"
This will result in displaying the values columns of table1 and next the column value2 from table2 where their key is the same.
Now i have another 2 tables which contain similar data and i want to check if the results of my query exists in the query i will build for the other tables like:
"select a.sth, a.sth2, a.st3, b.value for table3 a, table4 b where a.key = b.valkey"
The only way i thought of doing this was with nested implicit cursors. Like for example:
BEGIN
FOR item IN (select a.sth, a.sth2, a.st3, b.value for table1 a, table2 b where a.key = b.valkey)
LOOP
Begin
FOR item2 IN (select a.sth, a.sth2, a.st3, b.value for table3 a, table4 b where a.key = b.valkey)
LOOP
Begin
if (item1.sth = item2.sth) and (item1.sth2 = item2.sth2) and (item1.sth3 = item2.sth3) and (item1.value = item2.value) Then
dbms_output.put_line("Found and value is the same");
Elsif (item1.sth = item2.sth) and (item1.sth2 = item2.sth2) and (item1.sth3 = item2.sth3) and Not (item1.value = item2.value) Then
dbms_output.put_line("Found but value is different");
Exception When no_data_found then
dbms_output.put_line("item1 was not found in table3");
End;
END LOOP;
End;
END LOOP;
END;
The above is just pseudo code of what i thought to do. Can i do something like this or is there an alternative that has better performance which i can use? I am looking forward to your suggestions.

Answer 1

You don't need cursors for this. In general, set-based code is going to work better. The query would look something like this:
select coalesce(a.key, b.valkey) as thekey,
a.sth, a.sth2, a.st3, b.value
(case when a.key is null then 'Not found in a'
when b.key is null then 'Not found in b'
when (a.sth = b.sth) and (a.sth2 = b.sth2) and (a.sth3 = b.sth3) and
(a.value = b.value)
then 'Found and same'
when (a.sth = b.sth) and (a.sth2 = b.sth2) and (a.sth3 = b.sth3) and
(a.value <> b.value)
then 'Found and different'
else 'Other!!!'
end)
from table1 a full outer join
table2 b
on a.key = b.valkey