You don’t mention if the columns are nullable. If they are and you want the same semantics that the AVG
aggregate provides you can do (2008)
SELECT *,
(SELECT AVG(c)
FROM (VALUES(R1),
(R2),
(R3),
(R4),
(R5)) T (c)) AS [Average]
FROM Request
The 2005 version is a bit more tedious
SELECT *,
(SELECT AVG(c)
FROM (SELECT R1
UNION ALL
SELECT R2
UNION ALL
SELECT R3
UNION ALL
SELECT R4
UNION ALL
SELECT R5) T (c)) AS [Average]
FROM Request