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I have a table named Table1, with three fields Project ID, EmployeeID, Starting Date. Need a select statement to list all columns of the table, and an additional column to show the number of project by employee since a year. See below figure.

Existing table

It should be enough to get the count(distinct EmployeeID) where StartingDate > 1/1/2016. But, I can't figure out the query. Could anyone please help?

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If the project id is distinct this is easy to achieve with two window functions. Maybe not the best performance but just flows out of my fingers. Feel free to improve:

Setting up

CREATE TABLE #Table1
(
 ProjectID int,
 EmployeeID int,
 StartingDate DateTime
);

INSERT INTO #Table1 (ProjectID, EmployeeID, StartingDate)
VALUES (1, 1001, '1/1/2005'),
       (2, 1003, '1/1/2019'), 
       (3, 1007, '1/1/2012'),
       (4, 1001, '1/1/2017'),
       (5, 1002, '1/1/2018'), 
       (6, 1003, '1/1/2015'), 
       (7, 1001, '1/1/2016'), 
       (8, 1002, '1/1/2018'), 
       (9, 1004, '1/1/2018'), 
       (10, 10001, '1/1/2018');

The query;

WITH cte_Count
AS
(
  SELECT t.ProjectID,
         COUNT(*) OVER (PARTITION BY t.EmployeeID ORDER BY t.StartingDate) AS project_count
  FROM #Table1 t
  WHERE t.StartingDate > '1/1/2016'
)
SELECT t.ProjectID,
       t.EmployeeID,
       t.StartingDate,
       MAX(project_count) OVER (PARTITION BY t.EmployeeID) AS project_count_since_2016
FROM #Table1 t
LEFT JOIN cte_Count c ON c.ProjectID = t.ProjectID

The first part just filters the projects that are not in the range you want. The second joins this information with the source table.

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