Comments on: How to find the longest common substring patterns starting from the string head/tail

By: newkid

newkid — Fri, 25 Jun 2010 20:19:27 +0000

WITH t AS (
SELECT t5.*,MIN(LENGTH(in_str)) OVER(PARTITION BY grp_id) len FROM t5
)
SELECT DISTINCT id,grp_id,in_str
      ,MAX(CASE WHEN head_cnt=1 THEN head END) OVER(PARTITION BY grp_id)
      ,SUBSTR(MAX(CASE WHEN tail_cnt=1 THEN LPAD(rn,10)||tail END) OVER(PARTITION BY grp_id),11)
FROM (SELECT t2.*,COUNT(DISTINCT head) OVER(PARTITION BY grp_id,rn) head_cnt,COUNT(DISTINCT tail) OVER(PARTITION BY grp_id,rn) tail_cnt
        FROM (
      SELECT t.*,rn,SUBSTR(in_str,1,rn) head,SUBSTR(in_str,-rn) tail
        FROM t,(SELECT ROWNUM rn FROM (SELECT MAX(len) m FROM t) CONNECT BY ROWNUM<=m)
       WHERE rn<=t.len
             ) t2
      )
WHERE head_cnt=1 OR tail_cnt=1;

By: Maxim Demenko

Maxim Demenko — Thu, 05 Apr 2007 20:08:09 +0000

Well, here is another alternative (maybe not so elegant, but with supported packaged REVERSE function ) - using the table from previous example.

WITH t as
        (SELECT id, 
                grp_id, 
                in_str, 
                min(in_str) over (partition by grp_id) ref_str, 
                utl_raw.cast_to_raw(in_str) raw_str, 
                utl_raw.cast_to_raw(min(in_str) over (partition by grp_id)) ref_raw_str, 
                utl_raw.reverse(utl_raw.cast_to_raw(in_str)) reverse_raw_str, 
                utl_raw.reverse(utl_raw.cast_to_raw(min(in_str) over (partition by grp_id))) reverse_ref_raw_str 
        FROM    t5
        )
        , 
        t1 as 
        (SELECT id,
                grp_id,
                in_str,
                ref_raw_str,
                reverse_ref_raw_str, 
                min(nullif(utl_raw.compare(ref_raw_str,raw_str),0)) over(partition by grp_id)                  -1 head_len, 
                min(nullif(utl_raw.compare(reverse_ref_raw_str,reverse_raw_str),0)) over (partition by grp_id) -1 tail_len 
        FROM    t
        )
        , 
        t2 as 
        (SELECT id,
                grp_id,
                in_str, 
                utl_raw.substr(ref_raw_str,1,head_len) raw_head, 
                utl_raw.substr(reverse_ref_raw_str,1,tail_len) raw_tail 
        FROM    t1
        ) 
SELECT  id,
        grp_id,
        in_str, 
        utl_raw.cast_to_varchar2(raw_head)||'**'||utl_raw.cast_to_varchar2(utl_raw.reverse(raw_tail)) head_tail_pattern 
FROM    t2;

 ID  GRP_ID IN_STR               HEAD_TAIL_PATTERN
--- ------- -------------------- --------------------
  1      10 Fiveafpf1Three       Five**Three
  2      10 Five123zThree        Five**Three
  3      10 Five91OnezThree      Five**Three
  4      20 nine123TEN           nine**TEN
  5      20 nine345TEN           nine**TEN

By: Laurent Schneider

Laurent Schneider — Wed, 21 Mar 2007 12:34:43 +0000

note that REVERSE is not a supported function