Got it, let's tackle this problem since you can't use aggregate functions like LISTAGG (the usual go-to for string concatenation in DB2). We can use a recursive Common Table Expression (CTE) to build the comma-separated state string—this approach avoids aggregates entirely, relying on window functions and recursive logic instead.

Assumptions #

Let's assume your source table is named state_data with these columns:

• Element: VARCHAR (the grouping key that ties related state rows together)
• Value: VARCHAR (state codes like 'GA', 'CA', 'IL')

Step-by-Step Implementation #

1. Add ordered row numbers to each group: Use ROW_NUMBER() (a window function, not an aggregate) to assign a sequence to each state within its Element group. This gives us a clear order to build our concatenated string.
2. Recursively build the concatenated string: Start with the first state in each group, then recursively append each subsequent state with a comma separator.

Here's the full SQL code:

WITH numbered_rows AS (
    SELECT 
        Element,
        Value,
        ROW_NUMBER() OVER (PARTITION BY Element ORDER BY Value) AS rn
    FROM state_data
),
recursive_concat AS (
    -- Base case: Grab the first state for each Element as the starting string
    SELECT 
        Element,
        Value AS concatenated_values,
        rn
    FROM numbered_rows
    WHERE rn = 1
    
    UNION ALL
    
    -- Recursive step: Append the next state to the existing concatenated string
    SELECT 
        nr.Element,
        rc.concatenated_values || ',' || nr.Value AS concatenated_values,
        nr.rn
    FROM recursive_concat rc
    JOIN numbered_rows nr 
        ON rc.Element = nr.Element 
        AND nr.rn = rc.rn + 1
)
-- Final output: Pick the last row of each group (contains the full concatenated string)
SELECT 
    Element,
    concatenated_values AS Value
FROM recursive_concat
WHERE rn = (
    SELECT MAX(rn) 
    FROM numbered_rows 
    WHERE Element = recursive_concat.Element
);

How It Works #

• numbered_rows: This CTE adds a sequential number to each state in the same Element group. We order by Value here for consistent concatenation order, but you can tweak the ORDER BY clause (e.g., use a date column if you need insertion order).
• recursive_concat:
  • The base case initializes our concatenated string with the first state of each group.
  • The recursive step joins the previous result with the next row in the group, appending the new state with a comma.
• Final Select: We filter for the highest row number in each group—this gives us the complete comma-separated string of all states for that Element.

Quick Notes #

• If your Value column has NULLs, add WHERE Value IS NOT NULL in the numbered_rows CTE to skip empty entries.
• Adjust the VARCHAR lengths in your table schema to avoid truncating long concatenated strings.

内容的提问来源于stack exchange，提问作者Venky.m