MAX(age) seems safe enough -- no one gets any younger :-).

Combining MIN(name) and MAX(name) would allow one name change ... that should handle everyone, right!?

/*

insert into #temp(id,name)

select 2,'Jane Single'

insert into #temp(id,age)

select 2,28

insert into #temp(id,contact_number)

select 2,'123-456-7890'

insert into #temp(id,contact_number)

select 2,'987-654-3210'

insert into #temp(id,name)

select 2,'Jane Married'

*/

SELECT

tGroup.id, ca1.name, tGroup.age, t.contact_number

FROM (

SELECT id, MIN(name) AS name_min, MAX(name) AS name_max, MAX(age) AS age

FROM #temp

GROUP BY id

) AS tGroup

LEFT OUTER JOIN #temp t ON

t.id = tGroup.id

CROSS APPLY (

SELECT DISTINCT name

FROM (

SELECT name_min AS name UNION ALL

SELECT name_max

) AS derived

) AS ca1

WHERE

t.contact_number IS NOT NULL