SQL Coalesce with missing values - sql

Question

I have two tables, master and child. The master's primary key MM is an INT. The child table has a compound key of two columns and value column:
MM (INT)
POS (INT, values 1-32)
VV (INT, values 1-9)
Sample master table data:
(1, other data)
(2, other data)
(3, other data)
Sample child table data
(1, 1,2)
(1, 2,2)
(1, 4,1)
(1,15,1)
(2, 4,5)
(2, 5,3)
(2,31,7)
(3,3,1)
(4,18,2)
{4,19,5)
For a report I could like to de-normalize the data with an output like this:
(1,'22010000000000010000000000000000')
(2,'00053000000000000000000000000070')
(3,'00100000000000000000000000000000')
(4,'00000000000000000025000000000000')
I was thinking to use a select query with coalesce like this but the output is not not exactly what I want:
(1,'22110')
(2,'537')
(3,'1')
(4,'25')
How do I fill in the missing data with zeros?

Answer 1

One way I can think to do this uses a decimal value with a precision of 32 and sum() and then convert back to a zero-padded string:
select mm,
right(replicate('0', 32) + cast(sum(val) as varchar(32)), 32)
from (select c.*,
cast(cast(val as varchar(32)) + replicate('0', 32 - pos) as decimal(32, 0)) as val
from child c
) c
group by mm;
EDIT:
The above isn't generalizable (say, above 38 characters or to use letters as well as digits). Here is a more generalizable, but longer version:
select c.mm,
(max(case when pos = 1 then valc else '0' end) +
max(case when pos = 2 then valc else '0' end) +
max(case when pos = 3 then valc else '0' end) +
. . .
max(case when pos = 32 then valc else '0' end) +
)
from (select c.*, cast(val as varchar(255)) as valc
from child c
) c
group by c.mm;
I should note that if you want to handle a master with no children, then use a left join. That aspect of the problem seems less interesting than combining the values in the appropriate positions.

Answer 2

Try it like this
DECLARE #master TABLE(MM INT,OtherData VARCHAR(100));
INSERT INTO #master VALUES
(1, 'Other Data 1')
,(2, 'Other Data 2')
,(3, 'Other Data 3');
DECLARE #child TABLE(MM INT, POS INT, VV INT)
INSERT INTO #child VALUES
(1, 1,2)
,(1, 2,2)
,(1, 4,1)
,(1,15,1)
,(2, 4,5)
,(2, 5,3)
,(2,31,7)
,(3,3,1)
,(4,18,2)
,(4,19,5);
--One CTE to get 32 numbers
WITH Numbers(Nr) AS
(SELECT TOP 32 ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) FROM sys.objects) --get 32 numbers
--another CTE to get distinct MMs
,MMs AS
(
SELECT c.MM
,m.OtherData
FROM #child AS c
LEFT JOIN #master AS m ON c.MM=m.MM
GROUP BY c.MM,m.OtherData
)
--In this CTE The CROSS JOIN with the Numbers will create a list of 32 rows, which carry in all positions with a corresponding child its number. COALESCE will set a zero in the place of all NULLs
,Masked AS
(
SELECT MMs.MM
,MMs.OtherData
,Nr
,COALESCE(VV,0) AS Val
FROM MMs
CROSS JOIN Numbers
LEFT JOIN #child AS c1 ON c1.MM=MMs.MM AND c1.POS=Nr
)
-The final SELECT uses FOR XML PATH to get the 32 numbers in rows back to a string
SELECT *
,(
SELECT Masked.Val AS [*]
FROM Masked
WHERE Masked.MM=MMs.MM
FOR XML PATH('')
)
FROM MMs
The result
1 22010000000000100000000000000000
2 00053000000000000000000000000070
3 00100000000000000000000000000000
4 00000000000000000250000000000000