Analytic Function partition by

Question

I am almost where I want to be with this but lat steps are always killer.
I have a query that returns a list of ETL mappings/packages. The Source package (first one) can be identified with an ‘@’ in the string and all packages related to that mapping will follow (sorted by time).
I am stuck trying to propogate the name of this Source Mapping to all the packages below it until a change to the next Source.
Here’s an example of what I want
Source               Grp          Name
“sales@source”     1          Sales
salesa               0          Sales
slsb               0          Sales
“orders@hth”     1          Orders
ordersa          0          Orders
ordb               0          Orders
ordersc          0          Orders
“inventory@...     “ 1          Inventory
So my sql is basically showing how I am using Lag but it’s coming up short since I have to pre-determine the offset, which won’t work in this case.
SELECT source,
CASE WHEN source LIKE '%@%' THEN 1 ELSE 0 END GRP,
CASE WHEN
(CASE WHEN source LIKE '%@%' THEN 1 ELSE 0 END) =1
THEN substr (map_primary_source, 2, (instr(map_primary_source, '@')-3))
ELSE
lag(substr (map_primary_source, 2, (instr(map_primary_source, '@')-3)), 1,0)
over (ORDER BY creation_date)
END NAME,
creation_date
FROM table
WHERE creation_date > SYSDATE -1
ORDER BY creation_date
I’ve been trying different flavors of analytical functions (first value, over partition by, etc) but am coming up short.
By the way I am on 8.x

Answer 1

Yes, it works for variable numbers of rows.
Here is how to make your grp column and the solution all in one:
CREATE TABLE test AS (
    SELECT 'THIS@DESC' description, 'SALES' group_name FROM DUAL
    UNION
    SELECT 'THISa' description, 'SALES' group_name FROM DUAL
    UNION
    SELECT 'THISb' description, 'SALES' group_name FROM DUAL
    UNION
    SELECT 'THISc' description, 'SALES' group_name FROM DUAL
    UNION
    SELECT 'THISd' description, 'SALES' group_name FROM DUAL
    UNION
    SELECT 'THISe' description, 'SALES' group_name FROM DUAL
    UNION
    SELECT 'DEMO@DESC' description, 'DEMO' group_name FROM DUAL
    UNION
    SELECT 'DEMOa' description, 'DEMO' group_name FROM DUAL
    UNION
    SELECT 'DEMOb' description, 'DEMO' group_name FROM DUAL
    UNION
    SELECT 'THAT@DESC' description, 'THAT' group_name FROM DUAL
    UNION
    SELECT 'THATa' description, 'THAT' group_name FROM DUAL
    UNION
    SELECT 'THATb' description, 'THAT' group_name FROM DUAL
    UNION
    SELECT 'THATc' description, 'THAT' group_name FROM DUAL
    UNION
    SELECT 'WHERE@DESC' description, 'WHERE' group_name FROM DUAL
    UNION
    SELECT 'WHEREa' description, 'WHERE' group_name FROM DUAL
Table created.
SELECT * FROM test
DESCRIPTIO GROUP
DEMO@DESC  DEMO
DEMOa      DEMO
DEMOb      DEMO
THAT@DESC  THAT
THATa      THAT
THATb      THAT
THATc      THAT
THIS@DESC  SALES
THISa      SALES
THISb      SALES
THISc      SALES
THISd      SALES
THISe      SALES
WHERE@DESC WHERE
WHEREa     WHERE
SELECT
   FIRST_VALUE(description) OVER (PARTITION BY group_name ORDER BY group_num DESC) description,
   group_name
FROM
    SELECT
       description,
       CASE
          WHEN
             INSTR(description, '@') > 0
          THEN
             1
          ELSE
             0
       END group_num,
       group_name
    FROM
       test
DESCRIPTIO GROUP
DEMO@DESC  DEMO
DEMO@DESC  DEMO
DEMO@DESC  DEMO
THIS@DESC  SALES
THIS@DESC  SALES
THIS@DESC  SALES
THIS@DESC  SALES
THIS@DESC  SALES
THIS@DESC  SALES
THAT@DESC  THAT
THAT@DESC  THAT
THAT@DESC  THAT
THAT@DESC  THAT
WHERE@DESC WHERE
WHERE@DESC WHERE