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Comparing values in different rows

I need some advice regarding comparing values in different rows in the same table. For example:

Table X has columns A, B and C:
1 2 3
1 4 5
What I mean by comparison is that the values of B and C need to be reported (their values being non-equal).

As with most SQL questions, there are multiple ways to solve the problem. This one is no different. One way to do it would be to use an EXISTS predicate. First let's create and populate your table.

create table X
( A number,
  B number,
  C number

insert into X values (1, 2, 3);
insert into X values (1, 4, 5);
insert into X values (2, 6, 6);
insert into X values (2, 6, 6);
insert into X values (3, 1, 7);
insert into X values (3, 1, 9);
insert into X values (4, 8, 0);
If I understand your scenario correctly, you wish to only show those rows where the values in columns B and C don't match the values in columns B and C for other rows having the same value for column A. Here's a solution using EXISTS:
select * from X t
  where exists ( select * from X 
                   where A = t.A 
                     and ( B != t.B or C != t.C ) );

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