Count Distinct Window Function with Window Frame

Question

I'm trying to write a query to determine the number of unique users in a table over a rolling window of 30 days.

I figured I'd write something like this

select mydate, count(distinct users) 
over (order by mydate rows between 30 preceding and current row);

But this isn't supported in HP Vertica. Is there another way I can re-write the window frame naturally, without using window functions?

Answer 1

Something like this (you will get the idea - use function)

IF OBJECT_ID('[dbo].[MyUser]') IS NOT NULL
    DROP TABLE [dbo].[MyUser]

CREATE TABLE [dbo].[MyUser](    
    [Id] [int] IDENTITY(1,1) NOT FOR REPLICATION NOT NULL,
    MyDate DATETIME NOT NULL,
    Users INT NOT NULL
 CONSTRAINT [PK_MyUser] PRIMARY KEY CLUSTERED 
(
    [Id] ASC
)
)

GO

INSERT INTO [dbo].[MyUser] (MyDate, Users) 
SELECT DATEADD(DAY, -1, GETDATE()), 1
UNION ALL
SELECT DATEADD(DAY, -2, GETDATE()), 2
UNION ALL
SELECT DATEADD(DAY, -3, GETDATE()), 3
UNION ALL
SELECT DATEADD(DAY, -4, GETDATE()), 4
UNION ALL
SELECT DATEADD(DAY, -5, GETDATE()), 5
UNION ALL
SELECT DATEADD(DAY, -6, GETDATE()), 6
UNION ALL
SELECT DATEADD(DAY, -7, GETDATE()), 7
UNION ALL
SELECT DATEADD(DAY, -8, GETDATE()), 8
UNION ALL
SELECT DATEADD(DAY, -9, GETDATE()), 9
UNION ALL
SELECT DATEADD(DAY, -10, GETDATE()), 10

GO

IF OBJECT_ID (N'dbo.GetDistinctUsers', N'FN') IS NOT NULL
    DROP FUNCTION dbo.GetDistinctUsers;
GO

CREATE FUNCTION GetDistinctUsers (@StartDate DATETIME, @DateWindowSizeInDays INT)
RETURNS INT
WITH EXECUTE AS CALLER
AS
BEGIN
DECLARE @Users int;
SELECT @Users = COUNT(DISTINCT Users) FROM [dbo].[MyUser] WHERE DATEDIFF(DAY, @StartDate, MyDate) < @DateWindowSizeInDays
RETURN @Users 
END;
GO

select MyDate, dbo.GetDistinctUsers(MyDate, 2) FROM [MyUser]

instead DATEDIFF you can use anything you want to get desired results