Help With SQL Script

Question

Hi All ,
Here is my usecase. I have a table of following structure (History table):
    Column A - Unique key
    Column B - Foreign Key
    Start Date
    End Date.
  My Data is corrupted due to some reason .  Its supposed to be 
            StartDate         End Date
  1   MyID    2010-04-01         2013-10-07
  2   MyID    2013-10-07         3000-12-31
  It got corrupted and now it is
            StartDate         End Date
  1   MyID    2010-04-01         2013-10-07
  2   MyID    2010-04-01         3000-12-31
  Basically I want end date of first row to be updated as start date of second row. Because of some coding issue this corruption happened. 
  Now i want to find out all the cases for which this happened.
  I could find out all the rows for which multiple entries are there using :
  Select * from table where B in (
  Select B from table group by b having count(*) >1)
  But i need only corrupted records.  Can some one help me   ??
  Thanks in advance.
  B1

Answer 1

Since you have not provided proper data, hope below table format matches your record set.
WITH T1 AS
( SELECT  1 COL1, 1 COL2,  TO_DATE('2010-04-01','YYYY-MM-DD') START_DATE, TO_DATE('2013-10-07','YYYY-MM-DD') END_DATE FROM DUAL UNION ALL
  SELECT 2, 1,TO_DATE('2013-10-07','YYYY-MM-DD'),TO_DATE('2013-11-30','YYYY-MM-DD') FROM DUAL UNION ALL
  SELECT 3,1, TO_DATE('2013-10-07','YYYY-MM-DD'),TO_DATE('3000-12-31','YYYY-MM-DD') FROM DUAL UNION ALL
  SELECT 4,2,TO_DATE('2014-01-01','YYYY-MM-DD'), TO_DATE('2014-03-31','YYYY-MM-DD') FROM DUAL UNION ALL
  SELECT 5,2,TO_DATE('2014-01-01','YYYY-MM-DD'), TO_DATE('2014-12-31','YYYY-MM-DD') FROM DUAL)
  SELECT * FROM T1;
OUTPUT:
      COL1       COL2 START_DAT END_DATE
         1          1 01-APR-10   07-OCT-13
         2          1 07-OCT-13   30-NOV-13
         3          1 07-OCT-13   31-DEC-00
         4          2 01-JAN-14   31-MAR-14
         5          2 01-JAN-14   31-DEC-14
Seems like you look for records whose START_DATE is not matching with the previous record's END_DATE. The logic I have used is (according to your data), the START_DATE of RECORD1=START_DATE of RECORD2. This is what you are looking for. Below is the query.
WITH T1 AS
( SELECT  1 COL1, 1 COL2,  TO_DATE('2010-04-01','YYYY-MM-DD') START_DATE, TO_DATE('2013-10-07','YYYY-MM-DD') END_DATE FROM DUAL UNION ALL
  SELECT 2, 1,TO_DATE('2013-10-07','YYYY-MM-DD'),TO_DATE('2013-11-30','YYYY-MM-DD') FROM DUAL UNION ALL
  SELECT 3,1, TO_DATE('2013-10-07','YYYY-MM-DD'),TO_DATE('3000-12-31','YYYY-MM-DD') FROM DUAL UNION ALL
  SELECT 4,2,TO_DATE('2014-01-01','YYYY-MM-DD'), TO_DATE('2014-03-31','YYYY-MM-DD') FROM DUAL UNION ALL
  SELECT 5,2,TO_DATE('2014-01-01','YYYY-MM-DD'), TO_DATE('2014-12-31','YYYY-MM-DD') FROM DUAL)
  SELECT COL1,COL2,START_DATE,END_DATE FROM(
  SELECT COL1,COL2,START_DATE,END_DATE,
         LEAD(START_DATE) OVER(PARTITION BY COL2 ORDER BY COL1,COL2) LEAD_COL
  FROM T1)
  WHERE
  START_DATE = LEAD_COL
  OR LEAD_COL IS NULL;
OUTPUT:
      COL1       COL2 START_DAT END_DATE
         2          1 07-OCT-13 30-NOV-13
         3          1 07-OCT-13 31-DEC-00
         4          2 01-JAN-14 31-MAR-14
         5          2 01-JAN-14 31-DEC-14
Method 2 is also considering the condition END_DATE of record1 NOT EQUAL TO START_DATE OF record2.
WITH T1 AS
( SELECT  1 COL1, 1 COL2,  TO_DATE('2010-04-01','YYYY-MM-DD') START_DATE, TO_DATE('2013-10-07','YYYY-MM-DD') END_DATE FROM DUAL UNION ALL
  SELECT 2, 1,TO_DATE('2013-10-07','YYYY-MM-DD'),TO_DATE('2013-11-30','YYYY-MM-DD') FROM DUAL UNION ALL
  SELECT 3,1, TO_DATE('2013-10-07','YYYY-MM-DD'),TO_DATE('3000-12-31','YYYY-MM-DD') FROM DUAL UNION ALL
  SELECT 4,2,TO_DATE('2014-01-01','YYYY-MM-DD'), TO_DATE('2014-03-31','YYYY-MM-DD') FROM DUAL UNION ALL
  SELECT 5,2,TO_DATE('2014-01-01','YYYY-MM-DD'), TO_DATE('2014-12-31','YYYY-MM-DD') FROM DUAL)
  SELECT COL1,COL2,START_DATE,END_DATE FROM(
  SELECT COL1,COL2,START_DATE,END_DATE,LAG(END_DATE)OVER(PARTITION BY COL2 ORDER BY COL1,COL2) LAG_COL,
         LEAD(START_DATE) OVER(PARTITION BY COL2 ORDER BY COL1,COL2) LEAD_COL
  FROM T1)
  WHERE
  START_DATE!=LAG_COL
  OR START_DATE = LEAD_COL
  OR LAG_COL IS NOT NULL
  OR LEAD_COL IS NULL;
OUTPUT:
     COL1       COL2 START_DAT END_DATE
        2          1 07-OCT-13 30-NOV-13
        3          1 07-OCT-13 31-DEC-00
        4          2 01-JAN-14 31-MAR-14
        5          2 01-JAN-14 31-DEC-14