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sqlteradataolaprollupteradata-sql-assistant

Comparing TIMESTAMP data between previous row & current row using CASE statement and do operations according to the difference Teradata


I need help in constructing a query using Teradata(Version: 16.0+) OLAP functions with below scenario for comparing & eliminate rollup duplicates from a Teradata table.

I have below 9 records in a table ABC.

          Existing Data(Table - ABC)    


            ACCOUNT_ID  EXT_REF_NO  SERIAL_NUM  RECORD_START_DT RECORD_END_DT
        1   100000000002195 8495752450757852    341FE4E6A1AF    8/13/2019 12:24:42  8/20/2019 23:59:59
        2   100000000002195 8495752450757852    342FE4E6A1AF    8/21/2019 08:49:08  8/25/2019 23:59:59
        3   100000000002195 8495752450757852    343FE4E6A1AF    8/27/2019 02:42:46  8/26/2019 23:59:59
        4   100000000002195 8495752450757852    344FE4E6A1AF    8/28/2019 06:33:50  8/28/2019 23:59:59
        5   100000000002195 8495752450757852    345FE4E6A1AF    8/30/2019 02:35:32  8/31/2019 23:59:59
        6   100000000002195 8495752450757852    346FE4E6A1AF    9/2/2019 00:25:05   9/1/2019 23:59:59
        7   100000000002195 8495752450757852    347FE4E6A1AF    9/3/2019 03:33:28   9/3/2019 23:59:59
        8   100000000002195 8495752450757852    348FE4E6A1AF    9/4/2019 18:35:45   9/8/2019 23:59:59
        9   100000000002195 8495752450757852    349FE4E6A1AF    9/10/2019 11:22:54  3/16/2020 23:59:59

Output      

            ACCOUNT_ID  EXT_REF_NO  SERIAL_NUM  RECORD_START_DT RECORD_END_DT           
        1   100000000002195 8495752450757852    341FE4E6A1AF    8/13/2019 12:24:42  8/26/2019 23:59:59
        2   100000000002195 8495752450757852    342FE4E6A1AF    8/28/2019 06:33:50  8/28/2019 23:59:59
        3   100000000002195 8495752450757852    343FE4E6A1AF    8/30/2019 02:35:32  9/1/2019 23:59:59
        4   100000000002195 8495752450757852    345FE4E6A1AF    9/3/2019 03:33:28   9/8/2019 23:59:59
        5   100000000002195 8495752450757852    346FE4E6A1AF    9/10/2019 11:22:54  3/16/2020 23:59:59
  1. RECORD_END_DT should be always greater than RECORD_START_DT

  2. We will only consider those records for roll up where Record_start_dt of current row = (RECORD_END_DT + 1 day) for previous row, if the difference is more than 1 day it will not be considered

  3. You can find violating point 1 for row no - 3 & 6, this was actually a bug for same day expired records while data entry was done, you can virtually consider RECORD_START_DT as 8/26/2019 00:00:00 & 9/2/2019 00:00:00 respectively for row no - 3 & 6 for calculation

  4. ACCOUNT_ID,EXT_REF_NO,SERIAL_NUM all 3 should be considered for partition by

I have tried something like below. Only getting one row output with minimum DEVICE_START_DATE & maximum DEVICE_END_DATE like below:

ACCOUNT_ID EXT_REF SERIAL_NUM DEVICE_START_DATE DEVICE_END_DATE 100000000002195 8495752450757852 341FE4E6A1AF 8/13/2017 12:24:42.000000 9/16/2017 23:59:59.000000

 Query: SELECT 
      ACCOUNT_ID,
      EXT_REF, 
      SERIAL_NUM, 
      CASE WHEN (B.DIFF_DAYS <= 1 OR B.DIFF_DAYS IS NULL) THEN
      min(DEVICE_START_DATE) 
      OVER (PARTITION BY ACCOUNT_ID,EXT_REF,SERIAL_NUM order by 
      DEVICE_END_DATE desc)
      WHEN (B.DIFF_DAYS > 1 ) THEN
      min(DEVICE_START_DATE) 
      OVER (PARTITION BY ACCOUNT_ID,EXT_REF,SERIAL_NUM order by 
      DEVICE_END_DATE desc) 
      END AS DEVICE_START_DATE,
      DEVICE_END_DATE
      FROM
      (SELECT A.ACCOUNT_ID,
      A.EXT_REF, 
      A.SERIAL_NUM, 
      A.DEVICE_START_DATE, 
    A.DEVICE_START_DATE_VIRTUAL,
    A.DEVICE_END_DATE, 
    MIN(A.DEVICE_END_DATE)
    OVER ( PARTITION BY A.ACCOUNT_ID,A.EXT_REF,A.SERIAL_NUM ORDER BY A.DEVICE_END_DATE
    ROWS BETWEEN 1 PRECEDING AND 1 PRECEDING) AS DEVICE_END_DATE_PREVIOUS_ROW,
            TRUNC(A.DEVICE_START_DATE_VIRTUAL) - TRUNC(DEVICE_END_DATE_PREVIOUS_ROW) AS DIFF_DAYS
    FROM
    (SELECT 
    ACCOUNT_ID, 
    EXT_REF, 
    SERIAL_NUM, 
    DEVICE_START_DATE, 
    CASE WHEN DEVICE_START_DATE > DEVICE_END_DATE  
    THEN (DEVICE_START_DATE - INTERVAL '1' DAY)   
    ELSE DEVICE_START_DATE END AS DEVICE_START_DATE_VIRTUAL,
    DEVICE_END_DATE
    FROM NDW_XH_TEMP_TABLES.TEST) A) B
    QUALIFY
    ROW_NUMBER() 
    OVER (PARTITION BY ACCOUNT_ID,EXT_REF,SERIAL_NUM order by DEVICE_END_DATE desc) = 1;

Solution

  • You need nested OLAP-functions, this should work as expected:

    SELECT 
       ACCOUNT_ID
      ,EXT_REF_NO
      ,SERIAL_NUM
      ,Coalesce(Lag(next_start)
                Over (PARTITION BY ACCOUNT_ID, EXT_REF_NO
                      ORDER BY next_start NULLS LAST)
               ,min_start) AS RECORD_START_DT
    
    -- If your Teradata version doesn't support LAG/LEAD you must switch to the MAX version
    --  ,Coalesce(Max(next_start)
    --            Over (PARTITION BY ACCOUNT_ID, EXT_REF_NO
    --                  ORDER BY next_start NULLS LAST
    --                  ROWS BETWEEN 1 Preceding AND 1 Preceding)
    --           ,min_start) AS RECORD_START_DT
      ,RECORD_END_DT  
    FROM
     (
       SELECT
          ACCOUNT_ID
         ,EXT_REF_NO
         ,SERIAL_NUM
         ,RECORD_START_DT
         ,RECORD_END_DT
    
         -- to check for a gap
         ,Lag(fixed_start)
          Over (PARTITION BY ACCOUNT_ID, EXT_REF_NO
                ORDER BY fixed_start DESC) AS next_start
    --     ,Max(fixed_start)
    --      Over (PARTITION BY ACCOUNT_ID, EXT_REF_NO
    --            ORDER BY fixed_start DESC
    --            ROWS BETWEEN 1 Preceding AND 1 Preceding) AS next_start
    
         -- used in the outer COALESCE to get the min start for the 1st group
         ,Min(RECORD_START_DT)
          Over (PARTITION BY ACCOUNT_ID, EXT_REF_NO) AS min_start
    
         -- gap detection
         ,CASE WHEN Cast(RECORD_END_DT AS DATE) + 1 = Cast(next_start AS DATE) THEN 0 ELSE 1 END AS flag
       FROM
        ( -- fixing the bad data first
          SELECT t.*
            ,CASE WHEN RECORD_START_DT > RECORD_END_DT THEN RECORD_START_DT - INTERVAL '1' DAY ELSE RECORD_START_DT END AS fixed_start
          FROM tab AS t
        ) AS fixed_data
       QUALIFY flag = 1
     ) AS dt
    

    This looks for gaps, after applying flag = 1 the current row got the max end date and the previous row the matching start date. The outer Select finally adds the this start date to the current row.