I've been tasked with coming up with a means of translating the following data:
date category amount
1/1/2012 ABC 1000.00
2/1/2012 DEF 500.00
2/1/2012 GHI 800.00
2/10/2012 DEF 700.00
3/1/2012 ABC 1100.00
into the following:
date ABC DEF GHI
1/1/2012 1000.00
2/1/2012 500.00
2/1/2012 800.00
2/10/2012 700.00
3/1/2012 1100.00
The blank spots can be NULLs or blanks, either is fine, and the categories would need to be dynamic. Another possible caveat to this is that we'll be running the query in a limited capacity, which means temp tables are out. I've tried to research and have landed on PIVOT but as I've never used that before I really don't understand it, despite my best efforts to figure it out. Can anyone point me in the right direction?
Dynamic SQL PIVOT:
create table temp
(
date datetime,
category varchar(3),
amount money
)
insert into temp values ('1/1/2012', 'ABC', 1000.00)
insert into temp values ('2/1/2012', 'DEF', 500.00)
insert into temp values ('2/1/2012', 'GHI', 800.00)
insert into temp values ('2/10/2012', 'DEF', 700.00)
insert into temp values ('3/1/2012', 'ABC', 1100.00)
DECLARE #cols AS NVARCHAR(MAX),
#query AS NVARCHAR(MAX);
SET #cols = STUFF((SELECT distinct ',' + QUOTENAME(c.category)
FROM temp c
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
set #query = 'SELECT date, ' + #cols + ' from
(
select date
, amount
, category
from temp
) x
pivot
(
max(amount)
for category in (' + #cols + ')
) p '
execute(#query)
drop table temp
Results:
Date ABC DEF GHI
2012-01-01 00:00:00.000 1000.00 NULL NULL
2012-02-01 00:00:00.000 NULL 500.00 800.00
2012-02-10 00:00:00.000 NULL 700.00 NULL
2012-03-01 00:00:00.000 1100.00 NULL NULL
Dynamic SQL PIVOT
Different approach for creating columns string
create table #temp
(
date datetime,
category varchar(3),
amount money
)
insert into #temp values ('1/1/2012', 'ABC', 1000.00)
insert into #temp values ('2/1/2012', 'DEF', 500.00)
insert into #temp values ('2/1/2012', 'GHI', 800.00)
insert into #temp values ('2/10/2012', 'DEF', 700.00)
insert into #temp values ('3/1/2012', 'ABC', 1100.00)
DECLARE #cols AS NVARCHAR(MAX)='';
DECLARE #query AS NVARCHAR(MAX)='';
SELECT #cols = #cols + QUOTENAME(category) + ',' FROM (select distinct category from #temp ) as tmp
select #cols = substring(#cols, 0, len(#cols)) --trim "," at end
set #query =
'SELECT * from
(
select date, amount, category from #temp
) src
pivot
(
max(amount) for category in (' + #cols + ')
) piv'
execute(#query)
drop table #temp
Result
date ABC DEF GHI
2012-01-01 00:00:00.000 1000.00 NULL NULL
2012-02-01 00:00:00.000 NULL 500.00 800.00
2012-02-10 00:00:00.000 NULL 700.00 NULL
2012-03-01 00:00:00.000 1100.00 NULL NULL
I know this question is older but I was looking thru the answers and thought that I might be able to expand on the "dynamic" portion of the problem and possibly help someone out.
First and foremost I built this solution to solve a problem a couple of coworkers were having with inconstant and large data sets needing to be pivoted quickly.
This solution requires the creation of a stored procedure so if that is out of the question for your needs please stop reading now.
This procedure is going to take in the key variables of a pivot statement to dynamically create pivot statements for varying tables, column names and aggregates. The Static column is used as the group by / identity column for the pivot(this can be stripped out of the code if not necessary but is pretty common in pivot statements and was necessary to solve the original issue), the pivot column is where the end resultant column names will be generated from, and the value column is what the aggregate will be applied to. The Table parameter is the name of the table including the schema (schema.tablename) this portion of the code could use some love because it is not as clean as I would like it to be. It worked for me because my usage was not publicly facing and sql injection was not a concern. The Aggregate parameter will accept any standard sql aggregate 'AVG', 'SUM', 'MAX' etc. The code also defaults to MAX as an aggregate this is not necessary but the audience this was originally built for did not understand pivots and were typically using max as an aggregate.
Lets start with the code to create the stored procedure. This code should work in all versions of SSMS 2005 and above but I have not tested it in 2005 or 2016 but I can not see why it would not work.
create PROCEDURE [dbo].[USP_DYNAMIC_PIVOT]
(
#STATIC_COLUMN VARCHAR(255),
#PIVOT_COLUMN VARCHAR(255),
#VALUE_COLUMN VARCHAR(255),
#TABLE VARCHAR(255),
#AGGREGATE VARCHAR(20) = null
)
AS
BEGIN
SET NOCOUNT ON;
declare #AVAIABLE_TO_PIVOT NVARCHAR(MAX),
#SQLSTRING NVARCHAR(MAX),
#PIVOT_SQL_STRING NVARCHAR(MAX),
#TEMPVARCOLUMNS NVARCHAR(MAX),
#TABLESQL NVARCHAR(MAX)
if isnull(#AGGREGATE,'') = ''
begin
SET #AGGREGATE = 'MAX'
end
SET #PIVOT_SQL_STRING = 'SELECT top 1 STUFF((SELECT distinct '', '' + CAST(''[''+CONVERT(VARCHAR,'+ #PIVOT_COLUMN+')+'']'' AS VARCHAR(50)) [text()]
FROM '+#TABLE+'
WHERE ISNULL('+#PIVOT_COLUMN+','''') <> ''''
FOR XML PATH(''''), TYPE)
.value(''.'',''NVARCHAR(MAX)''),1,2,'' '') as PIVOT_VALUES
from '+#TABLE+' ma
ORDER BY ' + #PIVOT_COLUMN + ''
declare #TAB AS TABLE(COL NVARCHAR(MAX) )
INSERT INTO #TAB EXEC SP_EXECUTESQL #PIVOT_SQL_STRING, #AVAIABLE_TO_PIVOT
SET #AVAIABLE_TO_PIVOT = (SELECT * FROM #TAB)
SET #TEMPVARCOLUMNS = (SELECT replace(#AVAIABLE_TO_PIVOT,',',' nvarchar(255) null,') + ' nvarchar(255) null')
SET #SQLSTRING = 'DECLARE #RETURN_TABLE TABLE ('+#STATIC_COLUMN+' NVARCHAR(255) NULL,'+#TEMPVARCOLUMNS+')
INSERT INTO #RETURN_TABLE('+#STATIC_COLUMN+','+#AVAIABLE_TO_PIVOT+')
select * from (
SELECT ' + #STATIC_COLUMN + ' , ' + #PIVOT_COLUMN + ', ' + #VALUE_COLUMN + ' FROM '+#TABLE+' ) a
PIVOT
(
'+#AGGREGATE+'('+#VALUE_COLUMN+')
FOR '+#PIVOT_COLUMN+' IN ('+#AVAIABLE_TO_PIVOT+')
) piv
SELECT * FROM #RETURN_TABLE'
EXEC SP_EXECUTESQL #SQLSTRING
END
Next we will get our data ready for the example. I have taken the data example from the accepted answer with the addition of a couple of data elements to use in this proof of concept to show the varied outputs of the aggregate change.
create table temp
(
date datetime,
category varchar(3),
amount money
)
insert into temp values ('1/1/2012', 'ABC', 1000.00)
insert into temp values ('1/1/2012', 'ABC', 2000.00) -- added
insert into temp values ('2/1/2012', 'DEF', 500.00)
insert into temp values ('2/1/2012', 'DEF', 1500.00) -- added
insert into temp values ('2/1/2012', 'GHI', 800.00)
insert into temp values ('2/10/2012', 'DEF', 700.00)
insert into temp values ('2/10/2012', 'DEF', 800.00) -- addded
insert into temp values ('3/1/2012', 'ABC', 1100.00)
The following examples show the varied execution statements showing the varied aggregates as a simple example. I did not opt to change the static, pivot, and value columns to keep the example simple. You should be able to just copy and paste the code to start messing with it yourself
exec [dbo].[USP_DYNAMIC_PIVOT] 'date','category','amount','dbo.temp','sum'
exec [dbo].[USP_DYNAMIC_PIVOT] 'date','category','amount','dbo.temp','max'
exec [dbo].[USP_DYNAMIC_PIVOT] 'date','category','amount','dbo.temp','avg'
exec [dbo].[USP_DYNAMIC_PIVOT] 'date','category','amount','dbo.temp','min'
This execution returns the following data sets respectively.
Updated version for SQL Server 2017 using STRING_AGG function to construct the pivot column list:
create table temp
(
date datetime,
category varchar(3),
amount money
);
insert into temp values ('20120101', 'ABC', 1000.00);
insert into temp values ('20120201', 'DEF', 500.00);
insert into temp values ('20120201', 'GHI', 800.00);
insert into temp values ('20120210', 'DEF', 700.00);
insert into temp values ('20120301', 'ABC', 1100.00);
DECLARE #cols AS NVARCHAR(MAX),
#query AS NVARCHAR(MAX);
SET #cols = (SELECT STRING_AGG(category,',') FROM (SELECT DISTINCT category FROM temp WHERE category IS NOT NULL)t);
set #query = 'SELECT date, ' + #cols + ' from
(
select date
, amount
, category
from temp
) x
pivot
(
max(amount)
for category in (' + #cols + ')
) p ';
execute(#query);
drop table temp;
There's my solution cleaning up the unnecesary null values
DECLARE #cols AS NVARCHAR(MAX),
#maxcols AS NVARCHAR(MAX),
#query AS NVARCHAR(MAX)
select #cols = STUFF((SELECT ',' + QUOTENAME(CodigoFormaPago)
from PO_FormasPago
order by CodigoFormaPago
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
select #maxcols = STUFF((SELECT ',MAX(' + QUOTENAME(CodigoFormaPago) + ') as ' + QUOTENAME(CodigoFormaPago)
from PO_FormasPago
order by CodigoFormaPago
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
set #query = 'SELECT CodigoProducto, DenominacionProducto, ' + #maxcols + '
FROM
(
SELECT
CodigoProducto, DenominacionProducto,
' + #cols + ' from
(
SELECT
p.CodigoProducto as CodigoProducto,
p.DenominacionProducto as DenominacionProducto,
fpp.CantidadCuotas as CantidadCuotas,
fpp.IdFormaPago as IdFormaPago,
fp.CodigoFormaPago as CodigoFormaPago
FROM
PR_Producto p
LEFT JOIN PR_FormasPagoProducto fpp
ON fpp.IdProducto = p.IdProducto
LEFT JOIN PO_FormasPago fp
ON fpp.IdFormaPago = fp.IdFormaPago
) xp
pivot
(
MAX(CantidadCuotas)
for CodigoFormaPago in (' + #cols + ')
) p
) xx
GROUP BY CodigoProducto, DenominacionProducto'
t #query;
execute(#query);
The below code provides the results which replaces NULL to zero in the output.
Table creation and data insertion:
create table test_table
(
date nvarchar(10),
category char(3),
amount money
)
insert into test_table values ('1/1/2012','ABC',1000.00)
insert into test_table values ('2/1/2012','DEF',500.00)
insert into test_table values ('2/1/2012','GHI',800.00)
insert into test_table values ('2/10/2012','DEF',700.00)
insert into test_table values ('3/1/2012','ABC',1100.00)
Query to generate the exact results which also replaces NULL with zeros:
DECLARE #DynamicPivotQuery AS NVARCHAR(MAX),
#PivotColumnNames AS NVARCHAR(MAX),
#PivotSelectColumnNames AS NVARCHAR(MAX)
--Get distinct values of the PIVOT Column
SELECT #PivotColumnNames= ISNULL(#PivotColumnNames + ',','')
+ QUOTENAME(category)
FROM (SELECT DISTINCT category FROM test_table) AS cat
--Get distinct values of the PIVOT Column with isnull
SELECT #PivotSelectColumnNames
= ISNULL(#PivotSelectColumnNames + ',','')
+ 'ISNULL(' + QUOTENAME(category) + ', 0) AS '
+ QUOTENAME(category)
FROM (SELECT DISTINCT category FROM test_table) AS cat
--Prepare the PIVOT query using the dynamic
SET #DynamicPivotQuery =
N'SELECT date, ' + #PivotSelectColumnNames + '
FROM test_table
pivot(sum(amount) for category in (' + #PivotColumnNames + ')) as pvt';
--Execute the Dynamic Pivot Query
EXEC sp_executesql #DynamicPivotQuery
OUTPUT :
A version of Taryn's answer with performance improvements:
Data
CREATE TABLE dbo.Temp
(
[date] datetime NOT NULL,
category nchar(3) NOT NULL,
amount money NOT NULL,
INDEX [CX dbo.Temp date] CLUSTERED ([date]),
INDEX [IX dbo.Temp category] NONCLUSTERED (category)
);
INSERT dbo.Temp
([date], category, amount)
VALUES
({D '2012-01-01'}, N'ABC', $1000.00),
({D '2012-01-02'}, N'DEF', $500.00),
({D '2012-01-02'}, N'GHI', $800.00),
({D '2012-02-10'}, N'DEF', $700.00),
({D '2012-03-01'}, N'ABC', $1100.00);
Dynamic pivot
DECLARE
#Delimiter nvarchar(4000) = N',',
#DelimiterLength bigint,
#Columns nvarchar(max),
#Query nvarchar(max);
SET #DelimiterLength = LEN(REPLACE(#Delimiter, SPACE(1), N'#'));
-- Before SQL Server 2017
SET #Columns =
STUFF
(
(
SELECT
[text()] = #Delimiter,
[text()] = QUOTENAME(T.category)
FROM dbo.Temp AS T
WHERE T.category IS NOT NULL
GROUP BY T.category
ORDER BY T.category
FOR XML PATH (''), TYPE
)
.value(N'text()[1]', N'nvarchar(max)'),
1, #DelimiterLength, SPACE(0)
);
-- Alternative for SQL Server 2017+ and database compatibility level 110+
SELECT #Columns =
STRING_AGG(CONVERT(nvarchar(max), QUOTENAME(T.category)), N',')
WITHIN GROUP (ORDER BY T.category)
FROM
(
SELECT T2.category
FROM dbo.Temp AS T2
WHERE T2.category IS NOT NULL
GROUP BY T2.category
) AS T;
IF #Columns IS NOT NULL
BEGIN
SET #Query =
N'SELECT [date], ' +
#Columns +
N'
FROM
(
SELECT [date], amount, category
FROM dbo.Temp
) AS S
PIVOT
(
MAX(amount)
FOR category IN (' +
#Columns +
N')
) AS P;';
EXECUTE sys.sp_executesql #Query;
END;
Execution plans
Results
date
ABC
DEF
GHI
2012-01-01 00:00:00.000
1000.00
NULL
NULL
2012-01-02 00:00:00.000
NULL
500.00
800.00
2012-02-10 00:00:00.000
NULL
700.00
NULL
2012-03-01 00:00:00.000
1100.00
NULL
NULL
CREATE TABLE #PivotExample(
[ID] [nvarchar](50) NULL,
[Description] [nvarchar](50) NULL,
[ClientId] [smallint] NOT NULL,
)
GO
INSERT #PivotExample ([ID],[Description], [ClientId]) VALUES ('ACI1','ACI1Desc1',1008)
INSERT #PivotExample ([ID],[Description], [ClientId]) VALUES ('ACI1','ACI1Desc2',2000)
INSERT #PivotExample ([ID],[Description], [ClientId]) VALUES ('ACI1','ACI1Desc3',3000)
INSERT #PivotExample ([ID],[Description], [ClientId]) VALUES ('ACI1','ACI1Desc4',4000)
INSERT #PivotExample ([ID],[Description], [ClientId]) VALUES ('ACI2','ACI2Desc1',5000)
INSERT #PivotExample ([ID],[Description], [ClientId]) VALUES ('ACI2','ACI2Desc2',6000)
INSERT #PivotExample ([ID],[Description], [ClientId]) VALUES ('ACI2','ACI2Desc3', 7000)
SELECT * FROM #PivotExample
--Declare necessary variables
DECLARE #SQLQuery AS NVARCHAR(MAX)
DECLARE #PivotColumns AS NVARCHAR(MAX)
--Get unique values of pivot column
SELECT #PivotColumns= COALESCE(#PivotColumns + ',','') + QUOTENAME([Description])
FROM (SELECT DISTINCT [Description] FROM [dbo].#PivotExample) AS PivotExample
--SELECT #PivotColumns
--Create the dynamic query with all the values for
--pivot column at runtime
SET #SQLQuery =
N' -- Your pivoted result comes here
SELECT ID, ' + #PivotColumns + '
FROM
(
-- Source table should in a inner query
SELECT ID,[Description],[ClientId]
FROM #PivotExample
)AS P
PIVOT
(
-- Select the values from derived table P
SUM(ClientId)
FOR [Description] IN (' + #PivotColumns + ')
)AS PVTTable'
--SELECT #SQLQuery
--Execute dynamic query
EXEC sp_executesql #SQLQuery
Drop table #PivotExample
Fully generic way that will work in non-traditional MS SQL environments (e.g. Azure Synapse Analytics Serverless SQL Pools) - it's in a SPROC but no need to use as such...
-- DROP PROCEDURE IF EXISTS
if object_id('dbo.usp_generic_pivot') is not null
DROP PROCEDURE dbo.usp_generic_pivot
GO;
CREATE PROCEDURE dbo.usp_generic_pivot (
#source NVARCHAR (100), -- table or view object name
#pivotCol NVARCHAR (100), -- the column to pivot
#pivotAggCol NVARCHAR (100), -- the column with the values for the pivot
#pivotAggFunc NVARCHAR (20), -- the aggregate function to apply to those values
#leadCols NVARCHAR (100) -- comma seprated list of other columns to keep and order by
)
AS
BEGIN
DECLARE #pivotedColumns NVARCHAR(MAX)
DECLARE #tsql NVARCHAR(MAX)
SET #tsql = CONCAT('SELECT #pivotedColumns = STRING_AGG(qname, '','') FROM (SELECT DISTINCT QUOTENAME(', #pivotCol,') AS qname FROM ',#source, ') AS qnames')
EXEC sp_executesql #tsql, N'#pivotedColumns nvarchar(max) out', #pivotedColumns out
SET #tsql = CONCAT ( 'SELECT ', #leadCols, ',', #pivotedColumns,' FROM ',' ( SELECT ',#leadCols,',',
#pivotAggCol,',', #pivotCol, ' FROM ', #source, ') as t ',
' PIVOT (', #pivotAggFunc, '(', #pivotAggCol, ')',' FOR ', #pivotCol,
' IN (', #pivotedColumns,')) as pvt ',' ORDER BY ', #leadCols)
EXEC (#tsql)
END
GO;
-- TEST EXAMPLE
EXEC dbo.usp_generic_pivot
#source = '[your_db].[dbo].[form_answers]',
#pivotCol = 'question',
#pivotAggCol = 'answer',
#pivotAggFunc = 'MAX',
#leadCols = 'candidate_id, candidate_name'
GO;
In my below query I among others filter on specific values with NOT IN, which for most part works like it should, but one of the filtered values (not the others) still returns in the view, and I cannot figure out why this is happening .. the value that is returned is '76751219' .. Can anyone help me figure out why?
The query:
DECLARE #json NVARCHAR(MAX)
SET #json = (SELECT PHONE_DATA FROM EFP_JSON WHERE ID = 1)
SELECT PhoneNumber
FROM EFP_PhoneNumberSeries
WHERE REPLACE(PhoneNumber, ' ', '') NOT IN (
SELECT PhoneNumbers.Number
FROM OPENJSON(#json)
WITH (
Localnumber VARCHAR(50) '$.Localnumber',
Name VARCHAR(50) '$.Name',
Email VARCHAR(50) '$.Email',
PhoneNumbers nvarchar(max) '$.PhoneNumbers' AS JSON,
Phones nvarchar(max) '$.Phones' AS JSON
) as UserInfo
CROSS APPLY OPENJSON(PhoneNumbers)
WITH(
Number nvarchar(100) '$.Number',
LineName nvarchar(100) '$.LineName',
GotoLocalNumber nvarchar(100) '$.GotoLocalNumber',
BelongsTo nvarchar(100) '$.BelongsTo'
) as PhoneNumbers
CROSS APPLY OPENJSON(Phones)
WITH(
description nvarchar(100) '$.description'
) as description
) AND REPLACE(PhoneNumber, ' ', '') LIKE '767512%' OR REPLACE(PhoneNumber, ' ', '') LIKE '767520%'
AND LTRIM(REPLACE(PhoneNumber, ' ', '')) NOT IN ('76752000','76752005','76752006','76752007','76752008','76752010','76752011','76752012','76751219','76751221','76752022','76752058','76752060','76752063','76752097','76752098');
76751219 is being returned because it matches the REPLACE(PhoneNumber, ' ', '') LIKE '767512%' criteria regardless of the NOT IN filter.
To resolve this, you need to fix the parenthesis in the last few lines as you appear to be missing some. Based on what you've said, I think those lines should read
AND ( -- add this round opening bracket
REPLACE(PhoneNumber, ' ', '') LIKE '767512%'
OR REPLACE(PhoneNumber, ' ', '') LIKE '767520%'
) -- add this round closing bracket
AND LTRIM(REPLACE(PhoneNumber, ' ', '')) NOT IN ('76752000','76752005','76752006','76752007','76752008','76752010','76752011','76752012','76751219','76751221','76752022','76752058','76752060','76752063','76752097','76752098');
but you should review this yourself to make sure it meets your requirements for the AND & OR logic.
Code below from how to preserve column names on dynamic pivot is used to create dynamic pivot table.
If source table contains no data, sql error occurs since create table column list end with comma (there are no pivot columns).
How to fix this so that empty table is returned ?
To reproduce, remove insert commands
insert into sales values ( '2016-1-1', 'Ø 12.3/3mm', 2);
insert into sales values ( '2016-1-1', '+-3,4%/3mm', 52);
insert into sales values ( '2016-1-3', '/3,2m-', 246);
from code.
testcase:
create temp table sales ( saledate date, productname char(20), quantity int );
insert into sales values ( '2016-1-1', 'Ø 12.3/3mm', 2);
insert into sales values ( '2016-1-1', '+-3,4%/3mm', 52);
insert into sales values ( '2016-1-3', '/3,2m-', 246);
do $do$
declare
voter_list text;
begin
create temp table myyk on commit drop as
select saledate as kuupaev,
format ('"%s"', replace (upper(productname), ' ', '')) as tootjakood,
sum(quantity)::int as kogus
from sales
group by 1,2
;
drop table if exists pivot;
voter_list := (
select string_agg(distinct tootjakood, ' ' order by tootjakood) from myyk
);
execute(format('
create table pivot (
kuupaev date,
%1$s
)', (replace(voter_list, ' ', ' integer, ') || ' integer')
));
execute (format($f$
insert into pivot
select
kuupaev,
%2$s
from crosstab($ct$
select
kuupaev,tootjakood,kogus
from myyk
order by 1
$ct$,$ct$
select distinct tootjakood
from myyk
order by 1
$ct$
) as (
kuupaev date,
%4$s
);$f$,
replace(voter_list, ' ', ' + '),
replace(voter_list, ' ', ', '),
'',
replace(voter_list, ' ', ' integer, ') || ' integer' -- 4.
));
end; $do$;
select * from pivot;
Postgres 9.1 is used.
Insert an exception handler at the bottom of the DO block body. You can silently ignore errors and create dummy pivot table:
...
exception
when others then
drop table if exists pivot;
create table pivot ("No data" text);
end; $do$;
or raise an exception with your own error message:
...
exception
when others then
drop table if exists pivot;
raise exception 'There is no data in the source dataset.'
end; $do$;
You can also use if-then-else statement:
...
drop table if exists pivot;
if (select count(*) from myyk) > 0 then
voter_list := (
select string_agg(distinct tootjakood, ' ' order by tootjakood) from myyk
);
...
...
else
create table pivot ("No data" text);
end if;
end; $do$;
I have a table with four columns that I need to concat. Two of the columns contain some NULL values.
I need the result to contain separators indicating all four columns, like so:
colA,colB,colC,colD
or if one column (here colB) was null,
colA,,colC,colD
I can't seem to find a clean way to do this. The best I have come up with is:
concat_ws(colA, COALESCE(colB, ''), COALESCE(colC, ''), colD, ',')
This feels cumbersome (especially because I need to do this repeatedly). Is there a better way?
Since the final value can't be NULL, you don't need to worry about preserving them. Just use an empty string. This is how you'd write it in standard SQL.
select coalesce(cola, '') || ', ' ||
coalesce(colb, '') || ', ' ||
coalesce(colc, '') || ', ' ||
coalesce(cold, '')
from your_table_name;
The concat_ws() function doesn't skip empty strings, but it does skip null columns. That means you still have to use coalesce().
select concat_ws(', ', coalesce(cola, ''),
coalesce(colb, ''),
coalesce(colc, ''),
coalesce(colb, ''))
from your_table_name;
I think you should use a cursor and then a loop also, in order to show null values you must use a nvl() function, like this:
PROCEDURE TODO IS
vAux in VARCHAR2;
CURSOR CUR_TEST IN
SELECT NVL(colb, 'replace_with'), colA, colD
FROM DUAL;
Begin
for x in CUR_TEST loop
vAux := x.colb||','||x.colA||','||x.colD;
end loop;
end TODO;
For checking what nvl() does: http://www.techonthenet.com/oracle/functions/nvl.php