同時獲取每個列中每個值的計數

Question

我試圖看到類似的問題，但是沒有一個人在幫助解決這種有效的方法。

事情是我有一個帶有這樣的列的表：

我想計算表中每一列中值的出現次數，而不僅僅是表中的所有列。

我想得到這樣的東西：

p7     |  p7_count | p9 | p9_count
B      |   1       | A  |  2
A      |   1       | E  |  1
C      |   1      

但是我只能使用單個查詢來獲得此信息，例如：

SELECT p9, count(*) AS p9_Count
FROM respostas 
GROUP by p9
ORDER BY p9_Count DESC

但是我得到的結果是：

有沒有一種方法可以對所有列執行此操作，而不必分別為每個列執行操作並分別獲取結果？

Answer 1

您可以通過union all來做到這一點。 您到底想要什么還不清楚。 也許這很接近：

select p, max(p7cnt) as p7cnt, max(p8cnt) as p8cnt, max(p9cnt) as p9cnt
from ((select p7 as p, count(*) as p7cnt, 0 as p8cnt, 0 as p9cnt
       from respostas
       group by p7
      ) union all
      (select p8, 0 as p7cnt, count(*) as p8cnt, 0 as p9cnt
       from respostas
       group by p8
      ) union all
      (select p9, 0 as p7cnt, 0 as p8cnt, count(*) as p9cnt
       from respostas
       group by p9
      )
     ) ppp
group by p;

Answer 2

我認為這是您所描繪的那種東西。 它有點混亂，但是您可以通過添加合並來擴展它。 為了使其與row_number函數一起使用（對於MySQL），我將其轉換為使用子查詢。 當行數變大時，這將遠不是有效的，因為SQL不是此作業的正確工具。

select
    p1, p1_count, p2, p2_count, p3, p3_count
from
(
    select
        p1, p1_count,
        (
            select count(*) from
                (SELECT p1, count(*) AS p1_Count FROM respostas GROUP by p1) as t2
            where
                    t2.p1_Count <= t1.p1_Count
                or (t2.p1_Count  = t1.p1_Count and t2.p1 <= t1.p1)
        ) as rownum
    from (SELECT p1, count(*) AS p1_Count FROM respostas GROUP by p1) as t1
) as tt1

    full outer join

(
    select
        p2, p2_count,
        (
            select count(*) from
                (SELECT p2, count(*) AS p2_Count FROM respostas GROUP by p2) as t2
            where
                    t2.p2_Count <= t1.p2_Count
                or (t2.p2_Count  = t1.p2_Count and t2.p2 <= t1.p2)
        ) as rownum
    from (SELECT p2, count(*) AS p2_Count FROM respostas GROUP by p2) as t2
) as tt2
    on tt2.rownum = tt1.rownum

    full outer join

(
    select
        p3, p3_count,
        (
            select count(*) from
                (SELECT p3, count(*) AS p3_Count FROM respostas GROUP by p3) as t2
            where
                    t2.p3_Count <= t1.p3_Count
                or (t2.p3_Count  = t1.p3_Count and t2.p3 <= t1.p3)
        ) rownum
    from (SELECT p3, count(*) AS p3_Count FROM respostas GROUP by p2) as t3
) as tt3
    on tt3.rownum = coalesce(tt1.rownum, tt2.rownum)

order by
    coalesce(tt1.rownum, tt2.rownum, tt3.rownum)