c# - LINQ 查询获取每个其他值的最早条目

Question

假设我有一个包含大量股票报价的数据库

TableQuotes
2010-07-22 09:45:00.000, "ABC", 102.23
2010-07-22 09:45:00.000, "EFG", 24.65
2010-07-22 09:45:00.000, "HIJ", 14.20
2010-07-22 10:45:00.000, "ABC", 104.25
2010-07-22 10:45:00.000, "EFG", 26.09
2010-07-22 10:45:00.000, "HIJ", 12.43
2010-07-23 09:45:00.000, "ABC", 101.23
2010-07-23 09:45:00.000, "EFG", 23.65
2010-07-23 09:45:00.000, "HIJ", 16.20
2010-07-23 10:45:00.000, "ABC", 99.26
2010-07-23 10:45:00.000, "EFG", 22.09
2010-07-23 10:45:00.000, "HIJ", 11.43
...

我想知道如何编写一个查询:
1. 每天每个代码只抓取一个股票报价
2. 抓取每个品种每天最早的股票行情

例如，我的示例表的预期结果是:

Result
2010-07-22 09:45:00.000, "ABC", 102.23
2010-07-22 09:45:00.000, "EFG", 24.65
2010-07-22 09:45:00.000, "HIJ", 14.20
2010-07-23 09:45:00.000, "ABC", 101.23
2010-07-23 09:45:00.000, "EFG", 23.65
2010-07-23 09:45:00.000, "HIJ", 16.20

Answer 1

var result = from tq in TableQuotes
group tq by new {tq.TimeStamp.Date, tq.Symbol} into g
select g.OrderBy(tq => tq.TimeStamp).First();