Función para calcular la mediana en SQL Server

Si está utilizando SQL 2005 o mejor, este es un buen cálculo de mediana simple para una sola columna en una tabla:

SELECT
(
 (SELECT MAX(Score) FROM
   (SELECT TOP 50 PERCENT Score FROM Posts ORDER BY Score) AS BottomHalf)
 +
 (SELECT MIN(Score) FROM
   (SELECT TOP 50 PERCENT Score FROM Posts ORDER BY Score DESC) AS TopHalf)
) / 2 AS Median