Hantera NULL-värdet i UNPIVOT

Det här är fult men förlitar sig inte på att man måste hitta en out-of-band-ersättning för NULL :

declare @pivot_task table
(
age int null,
[a] numeric(8,2),
[b] numeric(8,2),
[c] numeric(8,2),
[d] numeric(8,2),
[e] numeric(8,2)
);

insert into @pivot_task values (18, 0.5, null, 0.6, 1.21, 1.52),
(19, 7.51, 6.51, 5.51, null, 3.53),
(20, 4.52, 4.52, 6.52, 3.53, null);


select a.age, pmu.[over], [av]
from (select 'a' as [over] union all select 'b' union all select 'c'
        union all select 'd' union all select 'e') pmu
cross join (select age from @pivot_task) as a
left join
@pivot_task pt
unpivot
(
 [av]
 for [over] in ([a], [b], [c], [d], [e])
) ex
on pmu.[over] = ex.[over] and
   a.age = ex.age

Resultat:

age         over av
----------- ---- ---------------------------------------
18          a    0.50
18          b    NULL
18          c    0.60
18          d    1.21
18          e    1.52
19          a    7.51
19          b    6.51
19          c    5.51
19          d    NULL
19          e    3.53
20          a    4.52
20          b    4.52
20          c    6.52
20          d    3.53
20          e    NULL

Men om du går den här vägen kan du ta bort UNPIVOT helt och hållet:

select a.age, pmu.[over],
      CASE pmu.[over]
           WHEN 'a' THEN a.a
           WHEN 'b' THEN a.b
           WHEN 'c' THEN a.c
           WHEN 'd' THEN a.d
           WHEN 'e' THEN a.e
        END [av]
from (select 'a' as [over] union all select 'b' union all select 'c'
        union all select 'd' union all select 'e') pmu
cross join @pivot_task as a