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CREATE TABLE dbo.GLProject
(project int, amount int, period date);
INSERT dbo.GLProject VALUES
(12345, 10, '20200101'),
(12345, 10, '20200201'),
(12345, 10, '20200301'),
(12345, 10, '20200401'),
(12345, 10, '20200501'),
(12345, 10, '20200601'),
(12345, 10, '20200901')/*,
(23456, 20, '20210901')*/;
DECLARE @d date = DATEFROMPARTS(YEAR(getdate()), MONTH(getdate()), 1);
;WITH src AS -- mostly your existing query
(
SELECT project,
period,
rn = ROW_NUMBER() OVER
(PARTITION BY project ORDER BY period DESC),
amount = SUM(SUM(amount)) OVER
(PARTITION BY project ORDER BY period
ROWS UNBOUNDED PRECEDING)
FROM dbo.GLProject
GROUP BY project, period
),
recur AS
(
SELECT project, period = DATEADD(MONTH, 1, period), amount
FROM src
WHERE rn = 1 AND period < @d
UNION ALL
SELECT project, DATEADD(MONTH, 1, period), amount
FROM recur WHERE period < @d
)
SELECT project, amount, period = CONVERT(char(6), period, 112)
FROM src
UNION ALL
SELECT project, amount, period = CONVERT(char(6), period, 112)
FROM recur
ORDER BY project, period;
