Mysql：獲取兩列中所有值的計數

Question

我有一個包含2列X，Y的表格。我想計算兩列中每條記錄的出現次數。 如：

X | Y 

A | A 
B | A 
B | C 
D | C 

結果應該是

variable | X_count | Y_count 
A  | 1  | 2 
B  | 2  | 0 
C  | 0  | 2 
D  | 1  | 0 

如何在mysql中實現這一目標？

編輯：好吧，花了幾個小時後，我確保Y中的所有值都是X的子集，即對於任何變量，X_count永遠不會爲0。這有助於優化嗎？

Answer 1

我想你需要通過

select v.variable, a.count(*), b.count(*) 
    from 
    (select x as variable 
    from my_table 
    union select y 
    from my_table) as v 
    inner join my_table as a on a.X = v.variable 
    inner join my_table as b on b.y = v.variable 
    group by v.variable 

事實上在Y工會臨時表和組是X的一個子集，允許以避免工會，然後但無論如何，我們需要不同的X

select v.variable, a.count(*), b.count(*) 
    from 
    (select distinct x as variable 
    from my_table) as v 
    inner join my_table as a on a.X = v.variable 
    inner join my_table as b on b.y = v.variable 
    group by v.variable 

Answer 2

select variable,count(x),count(y) from 
(select distinct x as variable,x,y from my_table 
union all 
select distinct y as variable, x,y from my_table)v 
group by variable order by variable;