查找组中出现次数最多的值

Question

我想找到每组中出现次数最多的值。

我尝试使用 top(k)(column) 但出现以下错误：列类不在聚合函数下且不在 GROUP BY 中。

例如：如果我有表 test_date 和 columns(pid, value)

pid, value
----------
1,a
1,b
1,a
1,c

我想要结果：

pid, value
----------
1,a

我试过SELECT pid,top(1)(value) top_value FROM test_data group by pid

I get the error: 

Column value  is not under aggregate function and not in GROUP BY

我也尝试过，anyHeavy()但它只适用于出现超过一半情况的值

Answer 1

此查询应该可以帮助您：

    SELECT
        pid,
        /*
        Decompose the query in parts:
        1. groupArray((value, count)): convert the group of rows with the same 'pid' to the array of tuples (value, count)
        2. arrayReverseSort: make reverse sorting by 'count' ('x.2' is 'count')
        3. [1].1: take the 'value' from the first item of the sorted array
        */
        arrayReverseSort(x -> x.2, groupArray((value, count)))[1].1 AS value
    FROM
    (
        SELECT
            pid,
            value,
            count() AS count
        FROM test_date
        GROUP BY
            pid,
            value
    )
    GROUP BY pid
    ORDER BY pid ASC