SQL查询，用于计算一列中值的总发生次数和另一列中的相对发生次数(SQL query to count total ocurrences of values in one column and relative occurrence in another column)

 这是我的第一篇文章，因此对格式/内容的任何一般性更正也是受欢迎的。 我对SQL比较陌生。 
 
 假设我有一个数据库，它从分类评估中收集测试结果。 我知道每个测试的预期结果是什么。 我还有一个列，指示测试是否成功，即返回的预期值与预期值匹配。 它看起来像这样： 
 
Expected_Result   Result    Success
   A                  A     True
   A                  B     False
   B                  B     True
   A                  A     True
   B                  A     False
 
 我知道我可以使用SELECT Expected_Result, COUNT(Expected_Result) FROM Evaluation_Results GROUP BY Expected_Result返回每个预期类型的​​总出现次数。 我知道如何使用SELECT COUNT(*) FROM Evaluation_Results WHERE Success = 'True' AND Expected_Result = 'A'特定预期结果的错误检测次数 
 
 我在努力的地方就是把两者结合起来。 我希望查询返回所有不同预期结果的列表，每个结果的总数，成功结果的数量以及总数的百分比，如下所示： 
 
Expected_Result     Total   Num_Successful  Success_Rate
A                    3          2             66.67
B                    2          1             50.00

This is my first post, so any general corrections to format/content are also welcome. I'm relatively new to SQL.
 
Say I have a database which collects test results from an classification evaluation. I know what the expected outcome is for each test. I also have a column indicating whether the test was successful, ie the expected value returned matched the expected value. It looks something like this:
 
Expected_Result   Result    Success
   A                  A     True
   A                  B     False
   B                  B     True
   A                  A     True
   B                  A     False
 
I know I can return the total occurrences of each expected type withSELECT Expected_Result, COUNT(Expected_Result) FROM Evaluation_Results GROUP BY Expected_Result. I know how to count the number of false detections for a specific expected outcome with SELECT COUNT(*) FROM Evaluation_Results WHERE Success = 'True' AND Expected_Result = 'A' 
 
Where I'm struggling is combining the two. I would like the query to return a list of all distinct expected results, the total of each, the count of successful results, and the percentage of the total, like so:
 
Expected_Result     Total   Num_Successful  Success_Rate
A                    3          2             66.67
B                    2          1             50.00

原文：https://stackoverflow.com/questions/38199178