Analytic sql question

Question

Dear All,
I have the following problem of getting the output table from the input table below.
Do you have any idea of doing this with the help of analytic sql?
p.s. I have done this by using pure plsql block which is too slow to run with high amount of data. Below data is just a sample, in real I have millions rows of data.
Input table:
TIME     USER     VALUE     
1     A     X
2     A     X
3     B     Y
4     B     Y
5     A     X
5     B     X
6     A     Y
7     B     Y
7     A     Y
Output table:
START_TIME     END_TIME     USER     VALUE
1          2          A     X
5          5          A     X
6          7          A     Y
3          4          B     Y
5          5          B     X
7          7          B     Y

Answer 1

I feel sure I've over-complicated things here, and that there's an easier way of doing it, but here's one solution:
with my_tab as (select 1 col1, 'A' col2, 'X' col3 from dual union all
                select 2 col1, 'A' col2, 'Y' col3 from dual union all
                select 3 col1, 'B' col2, 'Y' col3 from dual union all
                select 4 col1, 'B' col2, 'X' col3 from dual union all
                select 5 col1, 'A' col2, 'X' col3 from dual union all
                select 5 col1, 'B' col2, 'X' col3 from dual union all
                select 6 col1, 'A' col2, 'Y' col3 from dual union all
                select 7 col1, 'B' col2, 'Y' col3 from dual union all
                select 7 col1, 'A' col2, 'Y' col3 from dual)
select distinct start_col1,
                end_col1,
                first_value(col2) over (partition by col2, start_col1, end_col1 order by col1, start_col1, end_col1) col2,
                first_value(col3) over (partition by col2, start_col1, end_col1 order by col1, start_col1, end_col1) col3
from   (select col1,
               col2,
               col3,
               last_value(start_col1 ignore nulls) over (order by col1, col2) start_col1,
               last_value(end_col1 ignore nulls) over (order by col1 desc, col2 desc) end_col1
        from   (select col1,
                       col2,
                       col3,
                       case when lag(col2, 1, '{NULL}') over (order by col1, col2) <> col2
                                 then col1
                       end start_col1,
                       case when lead(col2, 1, '{NULL}') over (order by col1, col2) <> col2
                                 then col1
                       end end_col1
                from   my_tab))
order by col2,
         start_col1,
         end_col1;
START_COL1   END_COL1 C C
         1          2 A X
         5          5 A X
         6          7 A Y
         3          4 B Y
         5          5 B X
         7          7 B Y