Question

我正在尝试运行以下MS SQL查询：

 select PolicyCode, OccupancyCode, premiumcode, VersionNumber, rate
 from COVERAGE_RATES as cov
 group by PolicyCode, OccupancyCode, PremiumCode,VersionNumber, rate
 having (VersionNumber = 25 or VersionNumber = 
 (
     select MAX(versionnumber) from COVERAGE_RATES where
     PolicyCode = 4 and OccupancyCode=2 and PremiumCode = cov.PremiumCode
 ) ) and PolicyCode = 4
 AND OccupancyCode = 2

想法是记录VersionNumber为25的记录，或者如果组中没有这样的版本，则取最大数字。那就是我们有表：

policyCode Version ...
----------------------
1          2
1          10
2          1
2          25
2          26

我们应该得到以下结果：

policyCode Version ...
----------------------
1          10
2          25

Linq代码是：

var res = (from c in CoverageRate
                       group c by c.PolicyCode
                           into rateGroup
                           where rateGroup.Any(r => r.VersionNumber == versionNumber ||
                           r.VersionNumber == 
                           CoverageRate.Where(c2 => c2.OccupancyCode == occupancyCode && c2.PolicyCode == policyCode)
                               .Max(c2 => c2.VersionNumber))
                           select rateGroup);

但我想我做错了，因为当我尝试接受res.Count（）时出现以下错误：

无法创建类型'..CoverageRate'的常量值。在此上下文中仅支持原始类型（例如Int32，String和Guid'）。

有人可以帮我解决这个问题吗？

Answer 1

更新 - 我认为您正在寻找：

var res =  from c in CoverageRate
           group c by c.PolicyCode into rateGroup
           select rateGroup.OrderByDescending(x => x.VersionNumber)
                           .FirstOrDefault();

Answer 2

from c in CoverageRate
                       group c by c.PolicyCode
                           into g
                           select new
                        {
                            policyCode = g.Key,
                            Version = (from t2 in g select t2.VersionNumber).Max()
                        }

Linq：具有分组，有和Max的查询

2 个答案: