Everything_is_possible, Sql Server

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CREATE TABLE t(
   Customer INTEGER  NOT NULL PRIMARY KEY 
  ,[User]     VARCHAR(5) NOT NULL
  ,Revenue  INTEGER  NOT NULL
);
INSERT INTO t(Customer,[User],Revenue) VALUES
 (001,'James',500)
,(002,'James',750)
,(003,'James',450)
,(004,'Sarah',100)
,(005,'Sarah',500)
,(006,'Sarah',150)
,(007,'Sarah',600)
,(008,'James',150)
,(009,'James',100);

WITH cte AS
(
    SELECT *, ROW_NUMBER() OVER(PARTITION BY [User] ORDER BY Revenue DESC) AS rn
    FROM t    
), cte2 AS
(
    SELECT c.Customer, c.[User], c.[Revenue]
           ,percentile         = 1.0 * Revenue / c3.s
           ,running_percentile = 1.0 * c2.s / c3.s
    FROM cte c
    CROSS APPLY
         (SELECT SUM(Revenue) AS s
          FROM cte c2
          WHERE c.[User] = c2.[User]
            AND c2.rn <= c.rn) c2
    CROSS APPLY
         (SELECT SUM(Revenue) AS s
          FROM cte c2
          WHERE c.[User] = c2.[User]) AS c3
) 
SELECT *
FROM cte2 a
CROSS APPLY (SELECT MIN(running_percentile) AS rp
             FROM cte2
             WHERE running_percentile >= 0.8
               AND cte2.[User] = a.[User]) AS s
WHERE a.running_percentile <= s.rp;

View schema
Execution time: 0,03 sec, rows selected: 5, rows affected: 9, absolute service time: 0,2 sec