JavaSQLLite平均分数

Question

PreStatement = myConnection.prepareStatement(""
                        + "SELECT Game1.AVG(Score),Students.FirstName,Students.LastName "
                        + "FROM Game1 " 
                        + "INNER JOIN Students " 
                        + "ON Game1.StudentID = Students.StudentID " 
                        + "ORDER BY Students.FirstName ASC;");

这是一项艰巨的工作。（错误定义为平均分数部分）
但这是真的

PreStatement = myConnection.prepareStatement(""
                        + "SELECT AVG(Score),
                        + "FROM Game1 " 

是我做错了什么，还是我要做两次陈述才能得到平均分数

Answer 1

如果你想要每个学生的平均数，那么你应该使用GROUP BY：

SELECT AVG(g.Score), s.FirstName, s.LastName
FROM Game1 g INNER JOIN
     Students s
     ON g.StudentID = s.StudentID 
GROUP BY s.FirstName, s.LastName
ORDER BY s.FirstName ASC;

表别名还使查询更易于编写和读取

Answer 2

试试这个

PreStatement = myConnection.prepareStatement(""
                        + "SELECT AVG(Game1.Score),Students.FirstName,Students.LastName "
                        + "FROM Game1 " 
                        + "INNER JOIN Students " 
                        + "ON Game1.StudentID = Students.StudentID " 
                        + "ORDER BY Students.FirstName ASC;");