--


--

CREATE TABLE MinMax
(
	changeDate date,
	customerid integer,
	sales_before varchar(100),
	sales_after varchar(100)
)
GO


INSERT INTO MinMax 
VALUES 
( '20170706', 7000275, NULL, 'Amy Smith' ) ,
( '20170714', 7000275, 'Amy Smith', 'Unassigned' ) ,
( '20170718', 7000275, 'UnAssigned', 'Amy Smith' ) ,
( '20170706', 7000287, 'Unassigned', 'John West' ) ,
( '20170705', 7000333, NULL, 'Amy Smith' ) ,
( '20170613', 7000333, 'Amy Smith', 'Unassigned' ) ,
( '20170719', 7000333, 'UnAssigned', 'Joe west' ) ,
( '20170726', 7000333, 'Joe west', 'John Doe' )
GO

--


--

--
 
SELECT * FROM 
(
	SELECT Customerid , MIN(changeDate) FirstChangeDate , MAX(changeDate) LastChangeDate , COUNT(*)  NumberChanges FROM MinMax
	GROUP BY customerid
)k
CROSS APPLY
(
	SELECT TOP 1 sales_before FROM MinMax a
	WHERE a.customerid = k.customerid 
	ORDER BY changeDate
)r
CROSS APPLY
(
	SELECT TOP 1 sales_after FROM MinMax a
	WHERE a.customerid = k.customerid 
	ORDER BY changeDate
)r1

--