took this query from stackoverflow and substituted my values. But, there's no concept of 3 month rolling average.

;WITH cte (rn, username, move_in_date, Cnt_Lead_id) AS (

SELECT

rn = ROW_NUMBER() OVER (ORDER BY move_in_date),

username,

move_in_date,

Cnt_Lead_id

FROM [dbo].[countHistory]

)

SELECT

username,

move_in_date,

Cnt_Lead_id,

movagv = (

SELECT AVG(Cnt_Lead_id)

FROM cte AS inner_ref

WHERE inner_ref.rn BETWEEN outer_ref.rn-3 AND outer_ref.rn

)

FROM cte AS outer_ref

ORDER BY username, move_in_date

If you run this against the sampletable DDL you'll see it doesn't do 3 month rolling.