SQL Server 2019

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select char(11)


(No column name)





create table t(TheParts xml);

insert into t(TheParts)
select top(1000) replicate(cast('<x>AB</x><x>AB</x><x>AB</x><x/><x>AB</x><x/><x>AC</x><x>AB</x>' as nvarchar(max)),  100)
from sys.all_columns as a
cross join sys.all_columns as b
1000 rows affected

set statistics time on
select s.hierarchy into xyz
from t
cross apply
(
select string_agg(isnull(x, ''), ' | ') within group(order by rn) as hierarchy
from
(
    select rn, x, lead(x) over(order by rn) as n
    from
    (
    select row_number() over(order by n.x) as rn, n.x.value('text()[1]', 'varchar(20)') as x
    from t.TheParts.nodes('x') as n(x)
    ) as d
) as l
where isnull(x, char(1)) <> isnull(n, char(1))
) as s
SQL Server parse and compile time: 
   CPU time = 0 ms, elapsed time = 0 ms.

 SQL Server Execution Times:
   CPU time = 6766 ms,  elapsed time = 6781 ms.
1000 rows affected