SQL Query Find Row Differences

Question

Hello All!
This will most likely be a super-easy question and solution for some one.  Here is my scenario.
2 tables (Table_1, Table_2)
3 columns (A, B, C)
Table_1 has fewer records than Table_2, so I want to find the records in Table_2 that are not in Table_1I don't care to find records that are in Table_1 and not in Table_2
I will make the comparison only with Column A
For simplicity sake, lets say Table_1 has 10 total rows and Table_2 has 15 total rows.  It should only find the 5 rows that are in Table_2 and not in Table_1.  Therefore, if I add the number of records found in Table_2 to the total records in Table_1, then I should have at least the same amount of records in Table_1 and Table_2, if not more.  Also, is there a way where I can insert the row differences found into a 3rd "staging" table?
Example provided below.
Table_1
A | B | C
1 | blahblah | something
2 | blahblah | something
3 | blahblah | something
4 | blahblah | something
5 | blahblah | something
Table_2
A | B | C
1 | blahblah | something
3 | blahblah | something
5 | blahblah | something
6 | blahblah | something  <=== Difference
7 | blahblah | something  <=== Difference
In reality, there are millions of records in both tables.  I have a workaround for this, but it would require me to do this...Export the results from both Table_1 and Table_2.  Open both results in Excel and run a macro to find the difference.  Once I find the difference, I save it and import the results into the 3rd "staging" table.
Any help would be great!  Thanks!

Answer 1

SKP wrote:
But the op has asked for comparison with column A  only
Right, I missed that. Then you are right, we can use NULL adjusted NOT EXISTS:
with table_1 as(
                select 1 A,'ABC' B , 'XYZ' C from Dual UNION ALL
                select 2 A,'ABD' B , 'WYZ' C from Dual UNION ALL
                select 3 A,'ABE' B , 'VYZ' C from Dual
    table_2 as (
                select 1 A,'ABC' B , 'XYZ' C from Dual UNION ALL
                select 2 A,'ABD' B , 'WYZ' C from Dual UNION ALL
                select 3 A,'ABE' B , 'VYZ' C from Dual UNION ALL
                select 4 A,'ABF' B , 'UYZ' C from Dual UNION ALL
                select 5 A,'ABG' B , 'TYZ' C from Dual UNION ALL
                select null A,'ABG' B , 'TYZ' C from Dual
select  *
  from  table_2
  where not exists(
                   select  1
                     from  table_1
                     where table_1.a = table_2.a
                        or (table_1.a is null and table_2.a is null)
SY.
Message was edited by: Solomon Yakobson