Merging consecutive rows of a table

Question

I want to merge consecutive rows of a table. i.e. if my table has 4 rows of data then my ouput of query will have only 3 rows because
rows 1 and 2 are merged to first row of result
rows 2 and 3 are merged to second row of result
rows 3 and 4 are merged to third row of result
For example if my table is
A | B
1 | 4
9 | 7
3 | 2
7 | 9
then output of query should be
A | B |A1| B1
1 | 4 | 9 | 7
9 | 7 | 3 | 2
3 | 2 | 7 | 9
How can i write a query to achieve this?

Answer 1

If SortKey is B and we use DB2 or SQLServer2005,
we can emulate Lag and Lead.
for instance
create table LagLeadTable as
select 'AAAA' as Code,100 as SortKey,5 as Val from dual
union select 'AAAA',200,20 from dual
union select 'AAAA',300,15 from dual
union select 'AAAA',400,30 from dual
union select 'BBBB',500,60 from dual
union select 'BBBB',600,70 from dual
union select 'BBBB',610,90 from dual
union select 'BBBB',620,50 from dual
union select 'BBBB',630,70 from dual
union select 'CCCC',100,80 from dual;
select Code,SortKey,
Lag(Val,3,0)  over(partition by Code order by SortKey) as Lag3,
Lag(Val,2,0)  over(partition by Code order by SortKey) as Lag2,
Lag(Val,1,0)  over(partition by Code order by SortKey) as Lag1,
Val,
Lead(Val,1,0) over(partition by Code order by SortKey) as Lead1,
Lead(Val,2,0) over(partition by Code order by SortKey) as Lead2,
Lead(Val,3,0) over(partition by Code order by SortKey) as Lead3
  from LagLeadTable;Above query can be emulated by below query.
select Code,sortkey,
coalesce(max(Val) over(partition by Code order by SortKey
                  Rows between 3 preceding and 3 preceding),0) as Lag3,
coalesce(max(Val) over(partition by Code order by SortKey
                  Rows between 2 preceding and 2 preceding),0) as Lag2,
coalesce(max(Val) over(partition by Code order by SortKey
                  Rows between 1 preceding and 1 preceding),0) as Lag1,
Val,
coalesce(max(Val) over(partition by Code order by SortKey
                  Rows between 1 following and 1 following),0) as Lead1,
coalesce(max(Val) over(partition by Code order by SortKey
                  Rows between 2 following and 2 following),0) as Lead2,
coalesce(max(Val) over(partition by Code order by SortKey
                  Rows between 3 following and 3 following),0) as Lead3
  from LagLeadTable;my site :-)
http://www.geocities.jp/oraclesqlpuzzle/8-13.html