Concatenate Multiple Row Values into 1 Row, with SQL for iSeries

问题

First, I need to thank Kent Milligan and his article at http://www.mcpressonline.com/sql/techtip-combining-multiple-row-values-into-a-single-row-with-sql-in-db2-for-i.html for getting me as far in this problem as I have. But now I need to expand on what he has done here.

To avoid you having to go to his article, the problem he addressed was concatenating string data from multiple rows into a single row in the resulting table. For example:

Table Cars:

Make Model
Ford Fusion
Chevy Tahoe
Honda Odyssey
Ford Taurus
Ford Focus
Chevy Malibu

Results:

Make Model
Chevy Malibu, Tahoe
Ford Focus, Taurus, Fusion
Honda Odyssey

This was done with the SQL statement:

WITH numbered_sets(make, model, curr, prev) AS (
   SELECT make, model,
       ROW_NUMBER() OVER (PARTITION BY make ORDER BY model) AS curr,
       ROW_NUMBER() OVER (PARTITION BY make ORDER BY model) -1 AS prev
   FROM inventory)
SELECT make,
       MAX (TRIM(L ',' FROM
             CAST(SYS_CONNECT_BY_PATH(model, ',') AS VARCHAR(256)) ))
FROM numbered_sets
START WITH curr = 1
CONNECT BY make = PRIOR make AND prev = PRIOR curr
GROUP BY make

I was able to adapt that to my own table, and get most of the way where I wanted to get. But for my purposes, I have an additional column I need to include for the grouping. For example:

Table Cars:

Make Type Model
Ford Sedan Fusion
Chevy SUV Tahoe
Honda Minivan Odyssey
Ford Sedan Taurus
Ford Sedan Focus
Chevy Sedan Malibu
Ford SUV Escape
Ford SUV Explorer
Chevy Sedan Impala

For the Results, I’d be looking for:

Make Type Model
Chevy Sedan Malibu, Impala
Chevy SUV Tahoe
Ford Sedan Fusion, Taurus, Focus
Ford SUV Escape, Explorer
Honda Minivan Odyssey

Does anyone have any thoughts on what all I need to add to the original statement to be able to add the TYPE column, and GROUP on that accordingly? I’ve tried a handful of things, but I suspect I need to do something with the CONNECT_BY_PATH statement, I’m just not sure what.

Thank you

回答1:

I think you just need to integrate type at the correct points thoughtout the query.

without being able to test, I think this would be close; but I may have missed something...

WITH numbered_sets(make, type, model, curr, prev) AS (
   SELECT make, type, model,
       ROW_NUMBER() OVER (PARTITION BY make, Type ORDER BY Make, Type, model) AS curr,
       ROW_NUMBER() OVER (PARTITION BY make, type ORDER BY Make, type, model) -1 AS prev
   FROM inventory)
SELECT make, Type
       MAX (TRIM(L ',' FROM
             CAST(SYS_CONNECT_BY_PATH(model, ',') AS VARCHAR(256)) ))
FROM numbered_sets
START WITH curr = 1
CONNECT BY make = PRIOR make AND prev = PRIOR curr and type = prior type
GROUP BY make, type

Perhaps we need do change the connect by to do a concat before connect by... though I can't see why this would help yet...

CONNECT BY concat(make,type) = PRIOR concat(make,type) AND prev = PRIOR curr

来源：https://stackoverflow.com/questions/40467653/concatenate-multiple-row-values-into-1-row-with-sql-for-iseries

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