Merging 2 rows into one

Question

Greedings,
I have the following output
1       A       null     null
2      null      B         CHow is it possible to merge it into one line?
CREATE TABLE test_g
a VARCHAR2(1),
b VARCHAR2(1),
c VARCHAR2(1)
INSERT INTO test_g
VALUES (null,'B','C');
INSERT INTO test_g
VALUES ('A',null,null);

Answer 1

what you are asking of is a kind of Grouping?
If yes, you need to have a Grouping Trait, that stays common across the rows to be grouped.
Extending your example:
create table test_t (grp varchar2(5), col_a varchar2(5), col_b varchar2(5), col_c varchar2(5));
insert into test_t values ('A', 'A', null, null);
insert into test_t values ('A', null, 'B', null);
insert into test_t values ('A', null, null, 'C');
insert into test_t values ('B', 'B', null, null);
insert into test_t values ('B', null, null, 'D');
select grp, max(col_a), max(col_b), max(col_c)
  from test_t
group by grp;
GRP   MAX(COL_A) MAX(COL_B) MAX(COL_C)
A     A          B          C         
B     B                     D          If you do not have a Grouping Trait, then you can still simply merge the rows. To do this, remove the GRP column from Select and group by from above query; which I think answers your original question. However, would you want to club the data of entire table into a Single row? If not then you need a Grouping column (as demonstrated above).