Substitute Dense_Rank() value with Newid() value in TSQL? - tsql

Question

is it possible to substitute the value generated by Dense_Rank() with a Newid() value in TSQL? I use Dense_Rank() for grouping but I need a uniqueidentifier generated instead of an integer. Thanks in advance.

Answer 1

There's no direct way to do this, but as I mentioned in my comment, you can get your dense_rank() for each record, then generate a NEWID() for each distinct Dense_Rank(), then join it back to itself.
CREATE TABLE test(f1 int, f2 char(1));
INSERT INTO test
VALUES (1, 'a'),
(1, 'b'),
(1, 'c'),
(2, 'a'),
(2, 'b'),
(3, 'a'),
(3, 'd'),
(3, 'g');
With dr AS (SELECT f1, f2, dense_rank() OVER (PARTITION BY f1 ORDER BY f2) as dr FROM test)
,dr_newid AS (SELECT dr, newid() as nid FROM (SELECT dr FROM dr GROUP BY dr) as drsub)
SELECT dr.f1, dr.f2, dr.dr, dr_newid.nid
FROM dr LEFT OUTER JOIN dr_newid ON dr.dr = dr_newid.dr
ORDER BY f1, f2;
+----+----+----+--------------------------------------+
| f1 | f2 | dr | nid |
+----+----+----+--------------------------------------+
| 1 | a | 1 | 966389AF-4C70-4AA8-A5C9-6F9537B8A1B8 |
| 1 | b | 2 | 73BE2978-B7D7-46B8-8B04-3103C8410575 |
| 1 | c | 3 | CB935CCA-AFE5-4D13-9583-0440DF1BEFE2 |
| 2 | a | 1 | 966389AF-4C70-4AA8-A5C9-6F9537B8A1B8 |
| 2 | b | 2 | 73BE2978-B7D7-46B8-8B04-3103C8410575 |
| 3 | a | 1 | 966389AF-4C70-4AA8-A5C9-6F9537B8A1B8 |
| 3 | d | 2 | 73BE2978-B7D7-46B8-8B04-3103C8410575 |
| 3 | g | 3 | CB935CCA-AFE5-4D13-9583-0440DF1BEFE2 |
+----+----+----+--------------------------------------+
One caveat here though... depending on how your box performs the join from dr to dr_newid it may generate unique newids for each distinct dense_rank value. Using a LEFT JOIN should trick the optimizer into generating the dr_newid intermediate result set once to be joined back. An INNER JOIN though may not.
If it's giving incorrect results, you may dump that dr_newid out to a temp table and then join back, forcing the server to derive the newid() once for each distinct dense_rank() and avoid tricks to force the optimizer's logic.
sqlfiddle here