Migrate a Column into Multiple Columns - sql

Question

I have a table with the following columns 'ID, LIST_OF_VALUES'.
Example data is:
ID| LIST_OF_VALUES
--+----------------------------
1 | firstval-secondval-thirdval
2 | val1-val2
3 | val10-val20-val30
4 | singleval
I would like to select the data like this:
ID| VAL1 | VAL2 | VAL3
--+----------+-----------+-------
1 | firstval | secondval | thirdval
2 | val1 | val2 | NULL
3 | val10 | val20 | val30
4 | singlval | NULL | NULL
I am aware of the STRING_SPLIT function. I have tried using it in various ways with Cross Apply, but I can't seem to get the result I want.
I know I can do this using a mess of SUBSTR/INDEX, but I am just curious if STRING_SPLIT offers a more elegant solution.

Answer 1

Just another option
Example of XML Option
Select A.ID
,Val1 = tmpXML.value('/x[1]','varchar(100)')
,Val2 = tmpXML.value('/x[2]','varchar(100)')
,Val3 = tmpXML.value('/x[3]','varchar(100)')
from YourTable A
Cross Apply ( values ( Cast('<x>' + replace([LIST_OF_VALUES],'-','</x><x>')+'</x>' as xml) ) ) B(tmpXML)
Returns
ID Val1 Val2 Val3
1 firstval secondval thirdval
2 val1 val2 NULL
3 val10 val20 val30
4 singleval NULL NULL
Example of JSON Option - as suggested by #PanagiotisKanavos if 2016+
Select A.ID
,Val1 = JSON_VALUE(S,'$[0]')
,Val2 = JSON_VALUE(S,'$[1]')
,Val3 = JSON_VALUE(S,'$[2]')
from #YourTable A
Cross Apply ( values ( '["'+replace(replace([LIST_OF_VALUES],'"','\"'),'-','","')+'"]' ) ) B(S)

Answer 2

Assuming you don't have duplicates, you can use it . . . but it is not trivial:
select t.*, s.*
from t cross apply
(select max(case when seqnum = 1 then value end) as val1,
max(case when seqnum = 2 then value end) as val2,
max(case when seqnum = 3 then value end) as val3
from (select s.value,
row_number() over (order by charindex('-' + value + '-', '-' + t.list_of_values + '-') as seqnum
from string_split(t.list_of_values, '-') s
) s
) s;
Unfortunately, string_split() doesn't provide the ordering. This recreates it using charindex().

Answer 3

One simple and very efficient and scalable way would be to use an ordinal splitter such as dbo.DelimitedSplit8K (or dbo.DelimitedSplitN4K (for nchar/nvarchar). Then the query would be something like this
dbo.DelimitedSplit8K tvf
CREATE FUNCTION dbo.DelimitedSplit8K
--===== Define I/O parameters
(#pString VARCHAR(8000), #pDelimiter CHAR(1))
--WARNING!!! DO NOT USE MAX DATA-TYPES HERE! IT WILL KILL PERFORMANCE!
RETURNS TABLE WITH SCHEMABINDING AS
RETURN
--===== "Inline" CTE Driven "Tally Table" produces values from 1 up to 10,000...
-- enough to cover VARCHAR(8000)
WITH E1(N) AS (
SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL
SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL
SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1
), --10E+1 or 10 rows
E2(N) AS (SELECT 1 FROM E1 a, E1 b), --10E+2 or 100 rows
E4(N) AS (SELECT 1 FROM E2 a, E2 b), --10E+4 or 10,000 rows max
cteTally(N) AS (--==== This provides the "base" CTE and limits the number of rows right up front
-- for both a performance gain and prevention of accidental "overruns"
SELECT TOP (ISNULL(DATALENGTH(#pString),0)) ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) FROM E4
),
cteStart(N1) AS (--==== This returns N+1 (starting position of each "element" just once for each delimiter)
SELECT 1 UNION ALL
SELECT t.N+1 FROM cteTally t WHERE SUBSTRING(#pString,t.N,1) = #pDelimiter
),
cteLen(N1,L1) AS(--==== Return start and length (for use in substring)
SELECT s.N1,
ISNULL(NULLIF(CHARINDEX(#pDelimiter,#pString,s.N1),0)-s.N1,8000)
FROM cteStart s
)
--===== Do the actual split. The ISNULL/NULLIF combo handles the length for the final element when no delimiter is found.
SELECT ItemNumber = ROW_NUMBER() OVER(ORDER BY l.N1),
Item = SUBSTRING(#pString, l.N1, l.L1)
FROM cteLen l;
Query
select t.id,
max(case when ds.ItemNumber=1 then ds.Item end) as val1,
max(case when ds.ItemNumber=2 then ds.Item end) as val2,
max(case when ds.ItemNumber=3 then ds.Item end) as val3
from tTable t
cross apply
dbo.DelimitedSplit8K(t.LIST_OF_VALUES, '-') ds
group by t.id
order by t.id;
[EDIT] Here is an alternate method which produces the same output but does not use the DelimitedSplit8K function. This is the same approach as Gordon's but with an outer GROUP BY clause.
;with charindex_split_cte(id, Item, ItemNumber) as (
select t.id, sp.value,
row_number() over (order by charindex('-' + sp.value + '-', '-' + t.list_of_values + '-'))
from tTable t
cross apply string_split(t.list_of_values, '-') sp)
select id,
max(case when ItemNumber=1 then Item end) as val1,
max(case when ItemNumber=2 then Item end) as val2,
max(case when ItemNumber=3 then Item end) as val3
from charindex_split_cte
group by id
order by id;