Question

我需要从下表中获取max lesson_score，以及特定用户的相应日期：

--------------------------------
|uid |lesson_score |date       |
--------------------------------
|1   |2            |1391023460 |
|1   |8            |1391023518 |
|1   |4            |1391023596 |
--------------------------------

我需要一个结果：

---------------------------
|lesson_score |date       |
---------------------------
|8            |1391023596 |
---------------------------

我的SQL看起来像这样：

SELECT date, MAX(lesson_score) AS lesson_score 
FROM cdu_user_session_progress 
WHERE uid = 1 
GROUP BY date";

但它只给了我三行：

---------------------------
|lesson_score |date       |
---------------------------
|2            |1391023460 |
|4            |1391023596 |
|8            |1391023518 |
---------------------------

我做错了什么？谢谢！

Answer 1

SELECT date, MAX(lesson_score) AS lesson_score 
FROM cdu_user_session_progress 
WHERE uid = 1 
GROUP BY date";

MAX是一个聚合函数，如果有多个lesson_score值，它将返回lesson_score的最大值

在您的查询中，值始终相同，因此返回该值。请记住，SELECT MAX（...）不能对整个表记录起作用，它会逐个处理每个记录。

您可以使用此顺序获取结果

SELECT   top 1 date, lesson_score AS lesson_score 
FROM     cdu_user_session_progress 
WHERE    uid = 1 
ORDER BY lesson_score DESC;

Answer 2

尝试使用

SELECT lesson_score, date FROM cdu_user_session_progress ORDER BY lesson_score DESC LIMIT 1;

ORDER BY - 部分负责，最多。 lession_score将在开头提取。

在订购之后，您会得到以下结果：

---------------------------
|lesson_score |date       |
---------------------------
|8            |1391023518 |
|4            |1391023596 |
|2            |1391023460 |
---------------------------

现在LIMIT - 部分说，数据库应该只返回第一行 - 所有其他结果行将被忽略，结果如下：

---------------------------
|lesson_score |date       |
---------------------------
|8            |1391023518 |
---------------------------

为了获得最低分，你只需写ASC DESC的整数（或删除它，因为ASC是默认值）

Answer 3

为什么你想要这个小组？只需在您的查询中使用Order BY ColumnName DESC LIMIT 1，它就会返回所有记录，因为UID=1对所有记录都是真的，只是按日期对其进行分组，每个MAX显示DATE

Answer 4

SELECT [date], lesson_score
FROM cdu_user_session_progress
WHERE lesson_score = (SELECT MAX(lesson_score) FROM cdu_user_session_progress GROUP BY [ui] HAVING [uid] = 1)
    AND [uid] =1;

SQL：获取最大值及其对应的字段）

4 个答案: