從SQL到LINQ

Question

我想弄清楚如何將這個SQL select轉換爲LINQ，但我還沒有弄清楚它。

我得到每個Id（PersonId），每個測試，每個月，每年的最後一個測試記錄。基本上，每個人每年獲得本月的最後一個分數。

CREATE TABLE #MyTable 
(
    Id INT, 
    Score INT, 
    TestName VARCHAR(50), 
    TestDate DATETIME 
) 

INSERT INTO #MyTable 

VALUES 

(1, 10, 'Math', '2011-12-16 00:00:00.000') 

,(1, 25, 'Math', '2011-12-26 00:00:00.000') 

,(1, 100, 'Math', '2011-12-06 00:00:00.000') 

,(1, 10, 'Reading', '2011-12-16 00:00:00.000') 

,(1, 25, 'Reading', '2011-12-26 00:00:00.000') 

,(1, 100, 'Reading', '2011-12-06 00:00:00.000') 

,(2, 10, 'Math', '2011-12-16 00:00:00.000') 

,(2, 25, 'Math', '2011-12-26 00:00:00.000') 

,(2, 100, 'Math', '2011-12-06 00:00:00.000') 

,(2, 10, 'Reading', '2011-12-16 00:00:00.000') 

,(2, 25, 'Reading', '2011-12-26 00:00:00.000') 

,(2, 100, 'Reading', '2011-12-06 00:00:00.000') 

,(1, 10, 'Math', '2011-12-16 00:00:00.000') 

,(1, 25, 'Math', '2012-12-26 00:00:00.000') 

,(1, 100, 'Math', '2012-12-06 00:00:00.000') 

,(1, 10, 'Reading', '2012-12-16 00:00:00.000') 

,(1, 25, 'Reading', '2012-12-26 00:00:00.000') 

,(1, 100, 'Reading', '2012-12-06 00:00:00.000') 

,(2, 10, 'Math', '2012-12-16 00:00:00.000') 

,(2, 25, 'Math', '2012-12-26 00:00:00.000') 

,(2, 100, 'Math', '2012-12-06 00:00:00.000') 

,(2, 10, 'Reading', '2012-12-16 00:00:00.000') 

,(2, 25, 'Reading', '2012-12-26 00:00:00.000') 

,(2, 100, 'Reading', '2012-12-06 00:00:00.000') 



SELECT DISTINCT 
M.Id,M.Score,M.TestName, M.TestDate 

FROM 
#MyTable M 

WHERE 
M.TestDate IN (
SELECT MAX(m.TestDate) 
FROM #MyTable m 
GROUP BY MONTH(TestDate), YEAR(TestDate) 
) 

DROP TABLE 
#MyTable 

BEFORE子查詢：使用子查詢後

before image http://i43.tinypic.com/rkyps9.png

最終的結果，結果8個返回記錄：

SQL image http://i42.tinypic.com/b6rbpx.png

我有什麼：

from a in MyTable 
    where a.TestDate == from b in MyTable 
    group b.TestDate.Value.Month, 
     a.TestDate.Value.Year 

Answer 1

var q1= 
    from entry in MyTable 
    group entry by new{entry.TestDate.Month, entry.TestDate.Year} into g 
    select g.Where(entry => entry.TestDate == g.Max(e => e.TestDate)); 

請注意，這將爲每個月/年組合組創建組，這實際上可能更適合您的業務案例。如果你需要它雖然夷爲平地，你可以說：

var q2 = from g in q1 
     from entry in g 
     select entry; 

或：

var q2 = q1.SelectMany(g => g) 

Answer 2

試試這個：

from m in myTable 
where myTable 
    .GroupBy(x => new { x.TestDate.Month, x.TestDate.Year }) 
    .Select(grp => grp.Max(x => x.TestDate)) 
    .Any(x => x == m.TestDate) 
select new { m.Id, m.TestScore, m.TestName, m.TestDate };