SQL: how to get all the distinct characters in a column, across all rows

Question

Is there an elegant way in SQL Server to find all the distinct characters in a single varchar(50) column, across all rows?

Bonus points if it can be done without cursors :)

For example, say my data contains 3 rows:

productname
-----------
product1
widget2
nicknack3

The distinct inventory of characters would be "productwigenka123"

Answer 1

Here's a query that returns each character as a separate row, along with the number of occurrences. Assuming your table is called 'Products'

WITH ProductChars(aChar, remain) AS (
   SELECT LEFT(productName,1), RIGHT(productName, LEN(productName)-1) 
      FROM Products WHERE LEN(productName)>0
   UNION ALL
   SELECT LEFT(remain,1), RIGHT(remain, LEN(remain)-1) FROM ProductChars
      WHERE LEN(remain)>0
)
SELECT aChar, COUNT(*) FROM ProductChars
GROUP BY aChar

To combine them all to a single row, (as stated in the question), change the final SELECT to

SELECT aChar AS [text()] FROM
  (SELECT DISTINCT aChar FROM ProductChars) base
FOR XML PATH('')

The above uses a nice hack I found here, which emulates the GROUP_CONCAT from MySQL.

The first level of recursion is unrolled so that the query doesn't return empty strings in the output.

Answer 2

Use this (shall work on any CTE-capable RDBMS):

select x.v into prod from (values('product1'),('widget2'),('nicknack3')) as x(v);

Test Query:

with a as 
(
    select v, '' as x, 0 as n from prod 
    union all
    select v, substring(v,n+1,1) as x, n+1 as n from a where n < len(v)
)
select v, x, n from a -- where n > 0
order by v, n
option (maxrecursion 0)

Final Query:

with a as 
(
    select v, '' as x, 0 as n from prod 
    union all
    select v, substring(v,n+1,1) as x, n+1 as n from a where n < len(v)
)
select distinct x from a where n > 0
order by x
option (maxrecursion 0)

Oracle version:

with a(v,x,n) as 
(
    select v, '' as x, 0 as n from prod 
    union all
    select v, substr(v,n+1,1) as x, n+1 as n from a where n < length(v)
)
select distinct x from a where n > 0