Handle NULL value in UNPIVOT

问题

I'm able to unpivot a table but null values are not included in the result.

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

select * from pivot_task;

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 age, [over], [av]
from pivot_task
unpivot
(
 [av]
 for [over] in ([a], [b], [c], [d], [e])
) a;

You can see the result on http://sqlfiddle.com/#!6/2ab59/1 for 18 age [over] b and its null value is missing I want to include null as well for every null encounter.

I found replacing null with different value and then replacing all those constant different value approach is not feasible for my work. I want to include in unpivot only.

回答1:

This is ugly but doesn't rely on having to find an out-of-band replacement for 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

Result:

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

But if you're going down this route, you can eliminate the UNPIVOT entirely:

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

回答2:

Try this, it will replace all the null values with 10000000 before unpivot that is not an acceptable number in numeric(8,2), so the value will not exist already. Then the value will be replaced by null after unpivot:

;WITH x as
(
select 
age,
coalesce(cast(a as numeric(9,2)), 10000000) a,
coalesce(cast(b as numeric(9,2)), 10000000) b,
coalesce(cast(c as numeric(9,2)), 10000000) c,
coalesce(cast(d as numeric(9,2)), 10000000) d,
coalesce(cast(e as numeric(9,2)), 10000000) e
from pivot_task
)
select age, [over], nullif([av], 10000000) av
from x
unpivot
(
 [av]
 for [over] in ([a], [b], [c], [d], [e])
) a;

回答3:

USE ISNULL(columnname ,0) http://technet.microsoft.com/en-us/library/ms184325.aspx FOR ALL COLUMN BEFORE UNPIVOT IT.

like below.

Select Age, Data, Case When (Value = 0) Then NULL Else Value End Value
from (
select age, 
    ISNULL([a],0)[a], ISNULL([b],0)[b], ISNULL([c],0)[c], ISNULL([d],0)[d], ISNULL([e],0)[e]
From pivot_task) As pvttask
UnPivot ([Value] for [Data] In ([a], [b], [c], [d], [e])) a

来源：https://stackoverflow.com/questions/23238232/handle-null-value-in-unpivot