如何优化嵌套循环查询

Question

我有一个cte，我使用嵌套循环连接从3个不同的表中获取数据。性能非常慢，一段时间后我得到超时错误。我检查了查询计划，发现问题出在嵌套循环连接上。

如何优化以下查询？任何帮助/建议将不胜感激。

with DCT as(
    select distinct
           p.PolicyReference as PolicyNumber,
           Year(p.PolicyEffectiveDate) as PolicyYear,
           reverse(substring(reverse(p.PolicyReference) , 1 , 2 )) as 
           PolicySequence,
           p.PolicyEffectiveDate as InceptionDate,
           p.PolicyExpirationDate as ExpirationDate,
           p.AggregateLimitAmt_Orginal as AggregateLimit,
           p.AttachmentPointAmt_Orginal as AttachmentPoint,                   
           ch.DangerSignalDescription as DangerDescription,
           ct.TransactiomAmountOriginal,
           ch.PrimaryAllegation,
           p.LOBCode as GLLOBCode, 
           p.BusinessUnit as GLLOBName,
           p.ProducingOfficeCode as Office, 
           Null as CatCode,
           p.PolicyBasisCode as PolicyTrigger,
           Getdate() As ProcessDate,
    From [vwPolicy] p 
        Inner  Join [vwClaimHeader] ch  ON p.PolicyReference = ch.PolicyReference 
        Inner  Join [vwClaimTransactions] ct ON ch.ClaimSuffix = ct.ClaimSuffix)
select * from DCT;

我已附加查询计划执行，因为您可以看到嵌套循环占82％。我该如何克服这一点。这是一个非常直接的查询。