Mysql inner join 以连接数据为条件

Question

我有下表:

表学生:

id  name
1   foo
2   bar
3   baz

表格标记

student_id  mark  date
1           9     2011-08-10
1           20    2011-08-09
1           5     2011-08-08
2           12    2011-08-09
2           8     2011-08-10
3           10    2011-08-10

我希望每个学生都有他们的最后一个分数，即

foo 9
bar 8
baz 10

我怎样才能用 mysql 做到这一点？

编辑:这个例子的重点是如何在连接表上添加排序条件。

Answer 1

您将使用 GROUP BY 和 MAX 聚合函数来创建包含所有学生及其最新日期的记录集。然后可以将该记录集连接回原始表以检索所需的其他列。

The GROUP BY Statement

The GROUP BY statement is used in conjunction with the aggregate functions to group the result-set by one or more columns.

MAX([DISTINCT] expr)

Returns the maximum value of expr. MAX() may take a string argument; in such cases, it returns the maximum string value.

SQL语句

SELECT  s.name
        , m.Mark
FROM    student s
        INNER JOIN mark m ON m.student_id = s.id
        INNER JOIN (
          SELECT  s.id,
                  MAX(m.Date) as MaxDate
          FROM    student s
                  INNER JOIN mark m ON m.student_id = s.id
          GROUP BY
                  s.id
        ) sm ON sm.id = m.student_id AND sm.MaxDate = m.date