SQL Server - Include NULL using UNPIVOT - sql-server

Question

UNPIVOT will not return NULLs, but I need them in a comparison query. I am trying to avoid using ISNULL the following example (Because in the real sql there are over 100 fields):
Select ID, theValue, column_name
From
(select ID,
ISNULL(CAST([TheColumnToCompare] AS VarChar(1000)), '') as TheColumnToCompare
from MyView
where The_Date = '04/30/2009'
) MA
UNPIVOT
(theValue FOR column_name IN
([TheColumnToCompare])
) AS unpvt
Any alternatives?

Answer 1

To preserve NULLs, use CROSS JOIN ... CASE:
select a.ID, b.column_name
, column_value =
case b.column_name
when 'col1' then a.col1
when 'col2' then a.col2
when 'col3' then a.col3
when 'col4' then a.col4
end
from (
select ID, col1, col2, col3, col4
from table1
) a
cross join (
select 'col1' union all
select 'col2' union all
select 'col3' union all
select 'col4'
) b (column_name)
Instead of:
select ID, column_name, column_value
From (
select ID, col1, col2, col3, col4
from table1
) a
unpivot (
column_value FOR column_name IN (
col1, col2, col3, col4)
) b
A text editor with column mode makes such queries easier to write. UltraEdit has it, so does Emacs. In Emacs it's called rectangular edit.
You might need to script it for 100 columns.

Answer 2

It's a real pain. You have to switch them out before the UNPIVOT, because there is no row produced for ISNULL() to operate on - code generation is your friend here.
I have the problem on PIVOT as well. Missing rows turn into NULL, which you have to wrap in ISNULL() all the way across the row if missing values are the same as 0.0 for example.

Answer 3

I ran into the same problem. Using CROSS APPLY (SQL Server 2005 and later) instead of Unpivot solved the problem. I found the solution based on this article An Alternative (Better?) Method to UNPIVOT
and I made the following example to demonstrate that CROSS APPLY will NOT Ignore NULLs like Unpivot.
create table #Orders (OrderDate datetime, product nvarchar(100), ItemsCount float, GrossAmount float, employee nvarchar(100))
insert into #Orders
select getutcdate(),'Windows',10,10.32,'Me'
union
select getutcdate(),'Office',31,21.23,'you'
union
select getutcdate(),'Office',31,55.45,'me'
union
select getutcdate(),'Windows',10,null,'You'
SELECT OrderDate, product,employee,Measure,MeasureType
from #Orders orders
CROSS APPLY (
VALUES ('ItemsCount',ItemsCount),('GrossAmount',GrossAmount)
)
x(MeasureType, Measure)
SELECT OrderDate, product,employee,Measure,MeasureType
from #Orders orders
UNPIVOT
(Measure FOR MeasureType IN
(ItemsCount,GrossAmount)
)AS unpvt;
drop table #Orders

Answer 4

or, in SQLServer 2008 in shorter way:
...
cross join
(values('col1'), ('col2'), ('col3'), ('col4')) column_names(column_name)

Answer 5

Using dynamic SQL and COALESCE, I solved the problem like this:
DECLARE #SQL NVARCHAR(MAX)
DECLARE #cols NVARCHAR(MAX)
DECLARE #dataCols NVARCHAR(MAX)
SELECT
#dataCols = COALESCE(#dataCols + ', ' + 'ISNULL(' + Name + ',0) ' + Name , 'ISNULL(' + Name + ',0) ' + Name )
FROM Metric WITH (NOLOCK)
ORDER BY ID
SELECT
#cols = COALESCE(#cols + ', ' + Name , Name )
FROM Metric WITH (NOLOCK)
ORDER BY ID
SET #SQL = 'SELECT ArchiveID, MetricDate, BoxID, GroupID, ID MetricID, MetricName, Value
FROM
(SELECT ArchiveID, [Date] MetricDate, BoxID, GroupID, ' + #dataCols + '
FROM MetricData WITH (NOLOCK)
INNER JOIN Archive WITH (NOLOCK)
ON ArchiveID = ID
WHERE BoxID = ' + CONVERT(VARCHAR(40), #BoxID) + '
AND GroupID = ' + CONVERT(VARCHAR(40), #GroupID) + ') p
UNPIVOT
(Value FOR MetricName IN
(' + #cols + ')
)AS unpvt
INNER JOIN Metric WITH (NOLOCK)
ON MetricName = Name
ORDER BY MetricID, MetricDate'
EXECUTE( #SQL )

Answer 6

I've found left outer joining the UNPIVOT result to the full list of fields, conveniently pulled from INFORMATION_SCHEMA, to be a practical answer to this problem in some contexts.
-- test data
CREATE TABLE _t1(name varchar(20),object_id varchar(20),principal_id varchar(20),schema_id varchar(20),parent_object_id varchar(20),type varchar(20),type_desc varchar(20),create_date varchar(20),modify_date varchar(20),is_ms_shipped varchar(20),is_published varchar(20),is_schema_published varchar(20))
INSERT INTO _t1 SELECT 'blah1', 3, NULL, 4, 0, 'blah2', 'blah3', '20100402 16:59:23.267', NULL, 1, 0, 0
-- example
select c.COLUMN_NAME, Value
from INFORMATION_SCHEMA.COLUMNS c
left join (
select * from _t1
) q1
unpivot (Value for COLUMN_NAME in (name,object_id,principal_id,schema_id,parent_object_id,type,type_desc,create_date,modify_date,is_ms_shipped,is_published,is_schema_published)
) t on t.COLUMN_NAME = c.COLUMN_NAME
where c.TABLE_NAME = '_t1'
</pre>
output looks like:
+----------------------+-----------------------+
| COLUMN_NAME | Value |
+----------------------+-----------------------+
| name | blah1 |
| object_id | 3 |
| principal_id | NULL | <======
| schema_id | 4 |
| parent_object_id | 0 |
| type | blah2 |
| type_desc | blah3 |
| create_date | 20100402 16:59:23.26 |
| modify_date | NULL | <======
| is_ms_shipped | 1 |
| is_published | 0 |
| is_schema_published | 0 |
+----------------------+-----------------------+

Answer 7

Writing in May'22 with testing it on AWS Redshift.
You can use a with clause where you can coalesce the columns where nulls are expected. Alternatively, you can use coalesce in the select statement prior to the UNPIVOT block.
And don't forget to alias with the original column name (Not following won't break or violate the rule but would save some time for coffee).
Select ID, theValue, column_name
From
(select ID,
coalesce(CAST([TheColumnToCompare] AS VarChar(1000)), '') as TheColumnToCompare
from MyView
where The_Date = '04/30/2009'
) MA
UNPIVOT
(theValue FOR column_name IN
([TheColumnToCompare])
) AS unpvt
OR
WITH TEMP1 as (
select ID,
coalesce(CAST([TheColumnToCompare] AS VarChar(1000)), '') as TheColumnToCompare
from MyView
where The_Date = '04/30/2009'
)
Select ID, theValue, column_name
From
(select ID, TheColumnToCompare
from MyView
where The_Date = '04/30/2009'
) MA
UNPIVOT
(theValue FOR column_name IN
([TheColumnToCompare])
) AS unpvt

Answer 8

I had your same problem and this is
my quick and dirty solution :
your query :
select
Month,Name,value
from TableName
unpivot
(
Value for Name in (Col_1,Col_2,Col_3,Col_4,Col_5
)
) u
replace with :
select Month,Name,value from
( select
isnull(Month,'no-data') as Month,
isnull(Name,'no-data') as Name,
isnull(value,'no-data') as value from TableName
) as T1
unpivot
(
Value
for Name in (Col_1,Col_2,Col_3,Col_4,Col_5)
) u
ok the null value is replaced with a string, but all rows will be returned !!

Answer 9

ISNULL is half the answer. Use NULLIF to translate back to NULL. E.g.
DECLARE #temp TABLE(
Foo varchar(50),
Bar varchar(50) NULL
);
INSERT INTO #temp( Foo,Bar )VALUES( 'licious',NULL );
SELECT * FROM #temp;
SELECT
Col,
NULLIF( Val,'0Null' ) AS Val
FROM(
SELECT
Foo,
ISNULL( Bar,'0Null' ) AS Bar
FROM
#temp
) AS t
UNPIVOT(
Val FOR Col IN(
Foo,
Bar
)
) up;
Here I use "0Null" as my intermediate value. You can use anything you like. However, you risk collision with user input if you choose something real-world like "Null". Garbage works fine "!##34())0" but may be more confusing to future coders. I am sure you get the picture.