Question

我正在寻找以下SQL的Linq等价物：

SELECT t0.Fk_CompanyId, t0.CheckedUtc, t0.IsBlocking
  FROM MyTable t0
  LEFT OUTER JOIN MyTable t1
    ON t0.Fk_CompanyId = t1.Fk_CompanyId AND t0.CheckedUtc < t1.CheckedUtc
 WHERE t1.Fk_CompanyId IS NULL
   AND t0.CheckedUtc IS NOT NULL

我与Linq最亲密的是：

from t0 in MyTable
join t1 in MyTable on t0.Fk_CompanyId equals t1.Fk_CompanyId into t1tmp
from t1 in t1tmp.DefaultIfEmpty()
where t1.Fk_CompanyId == null && t0.CheckedUtc != null && t0.CheckedUtc < t1.CheckedUtc
select new { cid = t0.Fk_CompanyId, cuct = t0.CheckedUtc, isbl = t0.IsBlocking }

...产生以下SQL（稍微重新格式化）：

SELECT t0.Fk_CompanyId, t0.CheckedUtc, t0.IsBlocking
  FROM MyTable AS t0
  LEFT OUTER JOIN MyTable AS t1
    ON t0.Fk_CompanyId = t1.Fk_CompanyId
 WHERE (t1.Fk_CompanyId IS NULL)
   AND (t0.CheckedUtc IS NOT NULL)
   AND (t0.CheckedUtc < t1.CheckedUtc)

这些并不完全相同。（t0.CheckedUtc < t1.CheckedUtc被推送到WHERE。）当我在t0.CheckedUtc < t1.CheckedUtc上进行外部左连接时，这会在连接的右侧产生NULL值。当我使用WHERE进行过滤时，会删除我感兴趣的所有NULL值。

透视：我正在尝试使用最新的 CheckedUtc 查找 MyTable 中的行，如果有任何非NULL的行，则按 Fk_CompanyId <分组< / em>的。我想为每个 Fk_CompanyId 添加一行。有几个＆＃34;可能的重复＆＃34;只处理找到最新的CheckedUtc （但不是它们各自的行），或者假设 CheckedUtc 是非NULL。

所以：如何在Linq中对非等号谓词执行等效连接？

Answer 1

试试这个

from t0 in MyTable
From t1 in MyTable( x=>x.Fk_CompanyId=t0.Fk_CompanyId && x.CheckedUtc > t0.CheckedUtc ).DefaultIfEmpty()
where t1.Fk_CompanyId == null && t0.CheckedUtc != null 
select new { cid = t0.Fk_CompanyId, cuct = t0.CheckedUtc, isbl = t0.IsBlocking }

在Linq中使用非等于谓词的外连接的等价物

1 个答案: