選擇可能出現在多列中的結果的頻率（SQL）

Question

我有一張表，其中包含分佈在五個不同列上的名稱列表。我試圖獲得6個最常見的不同名稱。每個名稱只會出現在每個記錄中一次。五列是name_1，name_2 ... name_5。爲了名字，請將表格稱爲「mytable」。

任何幫助將不勝感激。

Answer 1

這裏有一個辦法：

SELECT name, COUNT(1) 
    FROM (   SELECT name_1 AS name FROM mytable 
     UNION ALL SELECT name_2 AS name FROM mytable 
     UNION ALL SELECT name_3 AS name FROM mytable 
     UNION ALL SELECT name_4 AS name FROM mytable 
     UNION ALL SELECT name_5 AS name FROM mytable 
     ) AS myunion 
GROUP BY name 
ORDER BY COUNT(1) DESC LIMIT 6 
; 

在表中有多少行呢？

Answer 2

試試這個：

SELECT iTable.iName, Count(iTable.iName) as TotalCount 
FROM 
(
    SELECT DISTINCT name_1 as iName FROM myTable 
     UNION 
    SELECT DISTINCT name_2 as iName FROM myTable 
     UNION 
    SELECT DISTINCT name_3 as iName FROM myTable 
     UNION 
    SELECT DISTINCT name_4 as iName FROM myTable 
     UNION 
    SELECT DISTINCT name_5 as iName FROM myTable 
) as iTable 
GROUP BY iTable.iName 
ORDER BY TotalCount DESC 
LIMIT 6 

Answer 3

您應該能夠從每個表中選擇所有名稱並將結果合併在一起。然後你可以計算每個名字出現的次數。

select * 
from 
(
    select name, count(*) 
    from (
    select name from table1 
    union all 
    select name from table2 
    union all 
    select name from table3 
    union all 
    select name from table4 
    union all 
    select name from table5 
) 
    group by name 
    order by count(*) desc 
) 
where rownum <= 6 

Answer 4

UNION + subselect在這種情況下應該爲你工作。

SELECT name_1, COUNT(*) FROM (
    SELECT name_1 FROM mytable 
    UNION ALL SELECT name_2 FROM mytable 
    UNION ALL SELECT name_3 FROM mytable 
    UNION ALL SELECT name_4 FROM mytable 
    UNION ALL SELECT name_5 FROM mytable 
) AS names GROUP BY name_1 ORDER BY 2 DESC LIMIT 6;