任何清潔劑或寫替代方法SQL連接腳本

Question

我有如下表：

Table2  
StudentNumbers ExamType 
------------------------ 
      1234   1 
      2343   2 
      3345   5 
      3454   1 
      5465   2 
      ... 

Table1 
StudentNumbers ExamType ExamDate School Area    Info 
------------------------------------------------------------------ 
      1234   1  0825 warren ny 0x504B03042D0 
      1234   1  0829 north nj 0x63D86E1FFFF 
      1233   2  0921 north nj 0xA001400646F 
      2343   1  0922 warren ny 0x01400646174 
      2343   1  0925 north ny 0x100100070se 
      ... 

我想編寫一個查詢得到以下結果：

StudentNumbers ExamType ExamDate School Area   Info 
----------------------------------------------------------------- 
      1234   1  0829 north nj 0x63D86E1FFFF 
      2343   1  0925 north ny 0x100100070se 

我寫了下面的查詢：

Select t1.StudentNumbers, t1.ExamDate, t1.School, t1.Info, t1.ExamType   
from Table1 as t1 
    Join(
     Select ts.StudentNumbers, max(ts.ExamDate) as ExamDate 
     from Table2 as ts 
     Join Table1 as pl on 
      ts.StudentNumbers = pl.StudentNumbers where ts.ExamType = pl.ExamType 
     group by ts.StudentNumbers 
     ) as t2 on t1.StudentNumbers = t2.StudentNumbers 
        and t1.ExamDate = t2.ExamDate 

上面的查詢工作，並給我我想要的結果是最大ExamDate基於表2的特定ExamType。但是在這個聚合方法中使用多個連接的最佳方式？或者有更清潔的選擇。

Answer 1

您的查詢是好的，但我認爲使用子查詢外的Table2表將是更好的選擇。

SELECT * 
FROM (
     SELECT StudentNumbers, ExamType, MAX(ExamDate) AS ExamDate 
     FROM Table1 
     GROUP BY StudentNumbers, ExamType 
    ) t1 JOIN Table1 t2 ON t1.StudentNumbers = t2.StudentNumbers 
      AND t1.ExamType = t2.ExamType AND t1.ExamDate = t2.ExamDate 
WHERE EXISTS(
      SELECT 1 
      FROM Table2 t3 
      WHERE t1.StudentNumbers = t3.StudentNumbers 
       AND t1.ExamType = t3.ExamType 
      ) 

Answer 2

SELECT 
    t1.* 
FROM Table1 t1 
INNER JOIN Table2 t2 
ON t1.StudentNumbers = t2.StudentNumbers 
WHERE t1.ExamDate = (SELECT MAX(ExamDate) FROM Table1 WHERE StudentNumbers = t1.StudentNumbers) 
ORDER BY t1.StudentNumbers ASC 

可能不是最有效的解決方案，但。