选择2列中的MAX最大值的计数

Question

This has been stumping me for a little bit and I can't seem to get the right query

Table 1:

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

What I'm looking for is the count of the max level of each unique record ie should return

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

etc.

Answer 1

You can use a sub-query to first determine the max levels and then do a count of the max levels, as below:

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

You need two steps, (1) find the max level for each record and (2) count the records that have that max level for each level. You can use a subquery to create the Record/MaxLevel table:

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

You may also want a third select to make sure you include all levels if you want 0 counts for levels that have no records with their value as the max level. You can select the distinct values for level as subquery 'a' and left join into the max level counts subquery '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

You need a subquery to extract maximum level for each record number. Then you outer query will count total appearances of each level as the maximum level.

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