Either directly or using a function (Different database engines might do this differently.)

Definition: The middle value in a distribution, above and below which lie an equal number of values.
(Taken from http://www.thefreedictionary.com/median)

Define "median". It has been years since I was taught statistics.
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I also take the chance to test whether there is support for SQL syntax hightlighting.
SELECT median FROM dual;

The following solution is credited to David Rozenshtein, Anatoly Abramovich, and Eugene Birger. More information can be found at http://www.oreilly.com/catalog/transqlcook/chapter/ch08.html.

To calculate the median of the light-bulb test results, use the following query:
SELECT x.Hours median
FROM BulbLife x, BulbLife y
GROUP BY x.Hours
HAVING
   SUM(CASE WHEN y.Hours [= x.Hours
      THEN 1 ELSE 0 END)]=(COUNT(*)+1)/2 AND
   SUM(CASE WHEN y.Hours >= x.Hours
      THEN 1 ELSE 0 END)>=(COUNT(*)/2)+1

I think thid willneed a little tuning to get the correct value if there are multiple(2) rows returned by the query given by ben