You can do it like this
SELECT pno, startdate + INTERVAL q.n - 1 DAY dates
FROM table1 t CROSS JOIN
(
SELECT a.N + b.N * 10 + 1 n
FROM
(SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) a
,(SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) b
ORDER BY n
) q
WHERE q.n - 1 <= DATEDIFF(enddate, startdate)
ORDER BY pno, dates
The subquery generates a sequence of numbers from 1 to 100. You can adjust it for your needs (if date differences span more or less than 100 days) or completely substitute it with a persisted tally(numbers) table if you do a lot of such queries.
Output:
+------+------------+
| pno | dates |
+------+------------+
| p1 | 2012-12-03 |
| p1 | 2012-12-04 |
| p1 | 2012-12-05 |
| p1 | 2012-12-06 |
| p2 | 2013-01-05 |
| p2 | 2013-01-06 |
| p2 | 2013-01-07 |
| p2 | 2013-01-08 |
| p3 | 2013-01-15 |
| p3 | 2013-01-16 |
| p3 | 2013-01-17 |
| p3 | 2013-01-18 |
| p3 | 2013-01-19 |
| p3 | 2013-01-20 |
+------+------------+
Here is SQLFiddle demo
UPDATE: To create and populate persisted tally table use
CREATE TABLE tally (n INT NOT NULL PRIMARY KEY);
INSERT INTO tally (n)
SELECT a.n + b.n * 10 + c.n * 100 + d.n * 1000 + 1 n
FROM
(SELECT 0 AS n UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) a
,(SELECT 0 AS n UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) b
,(SELECT 0 AS n UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) c
,(SELECT 0 AS n UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) d
ORDER BY n;
You'll have in the tally table sequence of numbers from 1 to 10000. That will allow you to work with date ranges that span more than 27 years.
Now the query boils down to
SELECT pno, startdate + INTERVAL q.n - 1 DAY dates
FROM table1 t CROSS JOIN tally q
WHERE q.n - 1 <= DATEDIFF(enddate, startdate)
ORDER BY pno, dates
Here is SQLFiddle demo