Dynamic SQL query with repeating elements - sql

Question

I am trying to build a query using dynamic sql which looks like following,
'select dense_rank () over(partition by column1 order by column1),
dense_rank () over(partition by column1,column2 order by column2),
dense_rank () over(partition by column1,column2,column3 order column3) from tablename'
I have used STUFF to build the query but able to create query only with one columns and could not repeat columns i.e.'partition by column1, column2'.
How to achieve this using STUFF or is there other way to do it ?

Answer 1

You can do it with two queries that concatenates string. One outer that builds the column list and one inner that builds the column list for the partition by clause.
Sample table:
create table T(C1 int, C2 int, C3 int);
Code:
declare #SQL nvarchar(max);
with C as
(
select C.name,
-- Use order by to control order of columns
row_number() over(order by C.column_id) as rn
from sys.columns as C
where object_id = object_id('T') -- Specify the name of the table
-- Optionally filter out any columns that
-- should not be included
)
select #SQL = 'select '+
stuff((
select ',dense_rank() over(partition by '+
stuff((
select ','+c2.name
from C as C2
where C2.rn <= C.rn
order by C2.rn
for xml path(''), type
).value('text()[1]', 'nvarchar(max)'), 1, 1, '') +
' order by '+C.name+')'
from C
for xml path(''), type
).value('text()[1]', 'nvarchar(max)'), 1, 1,'')+
' from T';
print #SQL;
--exec (#SQL);
Result:
select dense_rank() over(partition by C3 order by C3),
dense_rank() over(partition by C3,C2 order by C2),
dense_rank() over(partition by C3,C2,C1 order by C1)
from T
Note: STUFF (Transact-SQL) does not concatenate strings. It is used to insert one string into another string. In the code above, stuff is used to remove the leading comma in the concatenated string by inserting an empty string to the first position and overwriting 1 character. The actual concatenation is done by for xml.

Answer 2

Declare #col_name varchar(100)
Declare #colnm varchar(max)
Declare #multicol int
Declare #sqlstr varchar(max)
Declare Cur_1 cursor
for
Select name
from sys.columns
where object_id=object_id('tablename')
order by name
OPEN Cur_1
FETCH NEXT FROM Cur_1
INTO #col_name
set #colnm=''
set #multicol=0
WHILE ##FETCH_STATUS = 0
BEGIN
if #multicol=1
begin
set #colnm=#colnm + ',' + #col_name
end
else
begin
set #colnm= #colnm+ #col_name
end
if #multicol=0
begin
set #sqlstr='Select dense_rank () over(partition by ' + #colnm + ' order by ' + #colnm + '),'
end
else
begin
set #sqlstr=#sqlstr + char(13) + char(10) + 'dense_rank () over(partition by ' + #colnm + ' order by ' + #colnm + '),'
end
FETCH NEXT FROM Cur_1
INTO #col_name
set #multicol=1
END
CLOSE Cur_1;
DEALLOCATE Cur_1;
set #sqlstr=left(#sqlstr,len(#sqlstr)-1) + + char(13) + char(10) + 'from tablename'
print #sqlstr

Answer 3

Declare #QueryString Varchar(Max)
Declare #TblNm Varchar(100)
Set #TblNm='[dbo].[SampleTable]'
Set #QueryString=
(
Select ',dense_rank () over(partition by '+ ColNm + ' Order by [' + name + '])' + char(10) AS [text()]
From
(
SELECT name,ColNm = STUFF(
(
SELECT ',[' + name + ']'
FROM sys.columns
where object_id=object_id(#TblNm) and column_id<=Tbl1.column_id
FOR XML PATH ('')
), 1, 1, ''
)
FROM sys.columns Tbl1
where object_id=object_id(#TblNm)
) ColDtl
For XML PATH ('')
)
Set #QueryString='Select '
+ substring(#QueryString,2,len(#QueryString))
+ ' from ' + #TblNm
Select #QueryString as ExecString
--Exec (#QueryString)