想实现如下效果，就是分组后时间最⼤的那⼀条数据：
1、SQL
SELECT *
FROM ( SELECT * ,
ROW_NUMBER() OVER ( PARTITION BY RIP_GUID ORDER BY RU_CreatedTime DESC ) rn FROM RIP_FlowInfo ) t
WHERE t.rn <= 1;
2、LINQ
var groupQuery = from t in query group t by t.RIP_Guid into g select new { key = g.Key, source = g.OrderByDescending(tt => tt.RU_CreatedTime).FirstOrDefault() };
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