How to assign a unique identifier to the first n rows of a query in postgresql?

Question

In postgres SQL, how can I assign a unique identifier (rn?) to the first n rows of a query and a unique identifier to the n subsequent rows? The objective is to group by ticker and unique identifier, see actual vs expected screenshots for details.

Actual query

SELECT 
    *,
    SUM(eps_diluted) OVER (PARTITION BY ticker ORDER BY rn ASC ROWS BETWEEN CURRENT ROW AND 3 FOLLOWING) AS test_eps_diluted
FROM(
    SELECT 
        "PK",
        ticker,
        period_end_date,
        eps_diluted,
        ROW_NUMBER() OVER ( PARTITION BY ticker ORDER BY period_end_date DESC ) rn
    FROM "ANALYTICS"."vQUARTERLY_MASTER_MATERIALIZED" 
    --WHERE ticker = 'ACN' 
    ORDER BY ticker, period_end_date DESC
    ) q
ORDER BY ticker, period_end_date desc 

Actual result

Expected result

Answer 1

I found a workaround that works using a modulo. This solution allows me to SUM eps_diluted for the last most recent quarters, the subsequent 4 quarters, and so on. See Solution screenshot for details.

SELECT 
    * 
FROM (
    SELECT 
        *,
        SUM(eps_diluted) OVER (PARTITION BY ticker ORDER BY rn ASC ROWS BETWEEN CURRENT ROW AND 3 FOLLOWING) AS sum_eps_diluted,
        1+ ((rn - 1) % 4) AS modulo
    FROM(
        SELECT 
            "PK",
            ticker,
            period_end_date,
            eps_diluted,
            ROW_NUMBER() OVER ( PARTITION BY ticker ORDER BY period_end_date DESC ROWS BETWEEN CURRENT ROW AND 3 FOLLOWING) rn
        FROM "ANALYTICS"."vQUARTERLY_MASTER_MATERIALIZED" 
        ORDER BY ticker, period_end_date DESC
        ) t1
    --WHERE 1+ ((rn - 1) % 4) = 1
    ORDER BY ticker, period_end_date desc ) t2
WHERE modulo = 1

Solution