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如何在LINQ中执行以下操作

linq sql c#

Podge · 技术社区 · 16 年前

SELECT     a.Category, a.Description, a.Item, a.[Value], a.Loading, a.MaxDiscount, MIN(b.EffectiveDate) AS FromDate, a.EffectiveDate AS EndDate, a.SortOrder,  a.ID
FROM List a   
LEFT OUTER JOIN List b ON a.[Value] = b.[Value] AND a.Category = b.Category AND a.Description = b.Description AND a.Item = b.Item AND a.EffectiveDate < b.EffectiveDate  
GROUP BY a.Category, a.Description, a.Item, a.[Value], a.Loading, a.MaxDiscount, a.SortOrder, a.EffectiveDate, a.ID  
HAVING      (a.Category = 'General') AND (a.Description = 'Cover') AND (a.EffectiveDate <= CONVERT(DATETIME, '2009-04-01 00:00:00', 102)) AND (MIN(b.EffectiveDate) >= CONVERT(DATETIME, '2009-04-01 00:00:00', 102) OR MIN(b.EffectiveDate) IS NULL) AND (a.Item = 'Type')
ORDER BY a.SortOrder

var query = from a in List.All() join b in List.All() 
            on new {a.Value,a.Category ,a.Description,a.Item} 
            equals new {b.Value,b.Category ,b.Description,b.Item} into temp

我不知道如何添加a.EffectiveDate<b.当前生效日期

2 回复 | 直到 16 年前

Amy B 16 年前

如果你不加入,你就不必重组。如果你不加入,你就不必开玩笑了。

someDate = new DateTime(2009, 4, 1);

var query = 
from a in List
where a.Category == "General"
where a.Description == "Cover"
where a.Item == "Type"
where a.EffectiveDate < someDate
let minDate =
(
  from b in List
  where a.Value == b.Value
  where a.Category == b.Category
  where a.Description == b.Description
  where a.Item == b.Item
  where a.EffectiveDate < b.EffectiveDate
  orderby b.EffectiveDate
  select new DateTime? ( b.EffectiveDate )
).FirstOrDefault()
where !minDate.HasValue || someDate < minDate.Value
orderby a.SortOrder
select a;