Попробуйте:
SELECT
CONVERT(datetime, RIGHT(YourColumn,4)
+LEFT(YourColumn,4)
) AS ProperDateTime
FROM...
рабочий пример:
DECLARE @YourTable table (StringDate char(8))
INSERT @YourTable VALUES ('05102010')
INSERT @YourTable VALUES ('03182010')
SELECT
CONVERT(datetime, RIGHT(StringDate,4)
+LEFT(StringDate,4)
) AS ProperDateTime
FROM @YourTable
ВЫВОД:
ProperDateTime
-----------------------
2010-05-10 00:00:00.000
2010-03-18 00:00:00.000
(2 row(s) affected)