Question

这让我感到有点困难，我似乎无法获得正确的查询

表1：

╔════════════════════╗
║     Record   Level ║
╠════════════════════╣
║     1         0    ║
║     1         1    ║
║     1         2    ║
║     2         3    ║
║     2         4    ║
║     2         5    ║
║     3         2    ║
╚════════════════════╝

我正在寻找的是每条唯一记录的最高等级数，即应该返回

╔════════════════════╗
║ level 2, 2 records ║
║ level 5, 1 record  ║
╚════════════════════╝

等

Answer 1

您可以使用子查询首先确定最高级别，然后计算最高级别，如下所示：

SELECT
    max_level,
    count(*)
FROM
(
    SELECT
        max(level) AS max_level
    FROM table1
    GROUP BY Record
) max_levels
GROUP BY max_level
ORDER BY max_level;

Answer 2

您需要两个步骤，（1）找到每条记录的最高级别，以及（2）计算每个级别具有该最高级别的记录。您可以使用子查询来创建Record / MaxLevel表：

SELECT MaxLevel, COUNT(*) AS RecordCount
FROM (
        SELECT Record, MAX(Level) AS MaxLevel
        FROM Table1
        GROUP BY Record
    )
GROUP BY MaxLevel

您可能还需要第三个选择，以确保包含所有级别，如果您希望0级别没有记录，其值为最大级别。您可以选择级别的不同值作为子查询'a'，并将左连接选择为最大级别计数子查询'b'。

SELECT a.Level, COUNT(b.Record) AS RecordCount
FROM (SELECT DISTINCT Level FROM Table1) a
LEFT OUTER JOIN (
        SELECT Record, MAX(Level) AS MaxLevel
        FROM Table1
        GROUP BY Record
    ) b ON b.MaxLevel = a.Level
GROUP BY a.Level

Answer 3

您需要一个子查询来提取每个记录号的最大级别。然后，外部查询将计算每个级别的总体外观作为最大级别。

SELECT COUNT(*) AS c, Level FROM
(
    SELECT MAX(Level) AS Level
    FROM Table1 
    GROUP BY Record
) l
GROUP BY Level

Answer 4

select count(0), level
from table t
where level>= all (select level from table where t.record=record)
group by level

SELECT超过2列的MAX值

4 个答案: