;with
cte as
(
	select	EMPLOYEE, POSITION, EFFECT_DATE, END_DATE, 
		rn= row_number() over (partition by EMPLOYEE order by EFFECT_DATE)
	from	tbl
),
rcte as
(
	select	EMPLOYEE, POSITION, EFFECT_DATE, END_DATE, rn, grp = 1
	from	cte
	where	rn	= 1

	union all

	select	c.EMPLOYEE, c.POSITION, c.EFFECT_DATE, c.END_DATE, c.rn,
		grp	= case  when r.END_DATE = dateadd(day, -1, c.EFFECT_DATE)
				then r.grp
				else r.grp + 1
				end
	from	rcte r
		inner join cte c	on	r.EMPLOYEE = c.EMPLOYEE
                                        and     r.rn	   = c.rn - 1
)
select	EMPLOYEE, POSITION, EFFECT_DATE = min(EFFECT_DATE), END_DATE = max(END_DATE)
from	rcte
group by EMPLOYEE, POSITION, grp