Getting maximum length with the same pattern from a group of string

Question

I have a table of two columns. This table has 10 rows like this:
col1      col2
g1        abcdef
g1        abcdef-1
g1        abcdef-2-ghi
g1        abcde
g2        abc
g2        abcdefghijklmn
g2        abcdef
g2        acbdef
g2        abc
g2        abWhat I want is a query that will produce resultset like shown below
col1      col2
g1        abcde
g2        afor group g1 the result is abcde because that's the longest consecutive sequence of same characters (scanned from left to right) from all the strings that's grouped under g1. the same applies for g2. Anybody help? thanks.
Edited by: user9080476 on May 26, 2011 11:42 PM

Answer 1

Here's another complex solution. This one uses bit manipulation.
I'm not sure if it always works with non-ascii characters... too tired to check right now
WITH t AS (SELECT 'g1' AS col1, 'abcdef' AS col2 FROM DUAL
           UNION  ALL
           SELECT 'g1', 'abcdef-1' FROM DUAL
           UNION ALL
           SELECT 'g1', 'abcdef-2-ghi' FROM DUAL
           UNION ALL
           SELECT 'g1', 'abcde' FROM DUAL
           UNION  ALL
           SELECT 'g2', 'abc' FROM DUAL
           UNION  ALL
           SELECT 'g2', 'abcdefghijklmn' FROM DUAL
           UNION  ALL
           SELECT 'g2', 'abcdef' FROM DUAL
           UNION ALL
           SELECT 'g2', 'acbdef' FROM DUAL
           UNION  ALL
           SELECT 'g2', 'abc' FROM DUAL
           UNION  ALL
           SELECT 'g2', 'ab' FROM DUAL
           UNION  ALL
           /* some non-ASCII chars, just to make it more interesting... */
           SELECT 'g3', 'the quick brown fox òx€€' FROM DUAL
           UNION  ALL
           SELECT 'g3', 'the quick brown fox òx€ùè' FROM DUAL
           UNION ALL
           SELECT 'g3', 'the quick brown fox òx€à' FROM DUAL
           UNION ALL
           SELECT 'g4', null FROM DUAL
           UNION  ALL
           SELECT 'g4', 'the quick brown fox òx€ùè' FROM DUAL
           UNION ALL
           SELECT 'g4', 'the quick brown fox òx€à' FROM DUAL
           UNION  ALL
           SELECT 'g5', '€' FROM DUAL
           UNION ALL
           SELECT 'g5', '€' FROM DUAL
           UNION  ALL
           SELECT 'g6', 'abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzA' FROM DUAL
           UNION ALL
           SELECT 'g6', 'abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzABC' FROM DUAL
     t2 as (
             select
             t.*,
             rpad(col2,max(length(t.col2)) over(partition by t.col1)) as col2_pad from t
     t3 as (
           select
           t.col1,
           t.col2,
           utl_raw.bit_xor(utl_raw.cast_to_raw(t.col2_pad),
                      utl_raw.cast_to_raw(lag(t.col2_pad) over(partition by col1 order by col2))) as col2_xor from t2 t
            select
            distinct
            t.col1,
            -- t.col2,
            substrb(t.col2,1,
            floor(
            least(
               min(case when t.col2 is null then 0 else lengthb(t.col2) end) over(partition by t.col1) * 2,
            min(case when t.col2_xor is null then 9999999999999999
                      else regexp_instr(rtrim(t.col2_xor,'0'),'[1-9A-F]') end)
                           over (partition by t.col1) - 1)
            /2)
             from t3  t        
           order by 1,2