select PKID, DocumentID, DocumentWord, DocumentYear, Title, HurryLevelname, SecLevelname, SendTo,
titlename, isnull((convert(char(10),WriteDate,120)),'0000-00-00') as WriteDate from V_Office_SendStep
where LTRIM(RTRIM(DocumentID))<>'0'and DealFlag='0' and CancelFlag='0' and
(FlowFlag='0' or FlowFlag='1' or FlowFlag='10') and LTRIM(RTRIM(ReceiverList)) LIKE '%,120,%'
order by WriteDate desc
这是我的查询语句,请问对哪些字段做索引会提高查询速度?