SELECT Sum(fieldname)          AS fieldNameHere,
   Sum(Cast(error AS INT))  AS Error,
   Sum(jsperror)            AS JSPError,
   Sum(linkerror)       AS LinkError
FROM   schemaname.sessiondata session
WHERE  starttime >= :startTime0
   AND starttime < :endTime0
   AND fieldname = :fieldNameVal0
UNION ALL
SELECT Sum(fieldname)          AS fieldNameHere,
   Sum(Cast(error AS INT))  AS Error,
   Sum(jsperror)            AS JSPError,
   Sum(linkerror)       AS LinkError
FROM   schemaname.sessiondata session
WHERE  starttime >= :startTime1
   AND starttime < :endTime1
   AND fieldname = :fieldNameVal1
UNION ALL
SELECT Sum(fieldname)          AS fieldNameHere,
   Sum(Cast(error AS INT))  AS Error,
   Sum(jsperror)            AS JSPError,
   Sum(linkerror)       AS LinkError
FROM   schemaname.sessiondata session
WHERE  starttime >= :startTime2
   AND starttime < :endTime2
   AND fieldname = :fieldNameVal2

startTime0=Wed Sep 12 22:00:00 BST 2012
endTime0=Wed Sep 12 23:00:00 BST 2012
hitPrices0=1
startTime1=Wed Sep 12 23:00:00 BST 2012
endTime1=Thu Sep 13 00:00:00 BST 2012
hitPrices1=1
startTime2=Thu Sep 13 00:00:00 BST 2012
endTime2=Thu Sep 13 01:00:00 BST 2012
hitPrices2=1

SELECT Sum(fieldname)          AS fieldNameHere,
   Sum(Cast(error AS INT))  AS Error,
   Sum(jsperror)            AS JSPError,
   Sum(linkerror)       AS LinkError
FROM   schemaname.sessiondata session
WHERE  starttime >= '2012-09-12 22:00:00'
   AND starttime < '2012-09-12 23:00:00'
   AND fieldname = 1
UNION ALL
SELECT Sum(fieldname)          AS fieldNameHere,
   Sum(Cast(error AS INT))  AS Error,
   Sum(jsperror)            AS JSPError,
   Sum(linkerror)       AS LinkError
FROM   schemaname.sessiondata session
WHERE  starttime >= '2012-09-12 23:00:00'
   AND starttime < '2012-09-13 00:00:00'
   AND fieldname = 1
UNION ALL
SELECT Sum(fieldname)          AS fieldNameHere,
   Sum(Cast(error AS INT))  AS Error,
   Sum(jsperror)            AS JSPError,
   Sum(linkerror)       AS LinkError
FROM   schemaname.sessiondata session
WHERE  starttime >= '2012-09-13 00:00:00'
   AND starttime < '2012-09-13 01:00:00'
   AND fieldname = 1

[null, null, null, null]
[2, 1, 0, 0]
[null, null, null, null]

NULL    NULL    NULL    NULL
NULL    NULL    NULL    NULL
NULL    NULL    NULL    NULL