Question

我有一个包含2列X，Y的表。我想计算两列中每条记录的出现次数。例如：

X | Y

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

结果应为

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

如何在mysql中实现这一目标？

编辑：好的，花了几个小时后，我确保Y中的所有值都是X的子集。即对于任何变量，X_count永远不会为0。这有助于优化吗？

Answer 1

我认为你需要一个工会临时表和分组

  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

事实上Y是X的一个子集允许避免联合然后但是无论如何我们需要不同的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

Mysql：获取两列中所有值的计数

1 个答案: