mysql - 计算重复值 - 帮助我的 mysql 查询非常慢

Question

假设我有一个这样的表:

Id*|value

对于每个Id，我想计算相应的值存在的次数。就像这个示例数据一样:

1, a
2, b
3, a 
4, b
5, c
6, a

我想要:

1, a, 3
2, b, 2
3, a, 3
4, b, 2
5, c, 1
6, a, 3

这就是我现在所拥有的，我相信它正在工作，但速度非常慢:

SELECT t1.Id, t1.value, COUNT(t2.value) FROM `table` AS t1
LEFT JOIN `table` AS t2 ON (t1.value = t2.value)
GROUP by t1.Id

我的表包含数千行。关于如何提高这种性能有什么建议吗？

Answer 1

试试这个

SELECT t1.Id, t1.value, t2.cnt FROM Table1 AS t1
INNER JOIN 
(
  SELECT value, COUNT(value) as cnt 
    FROM Table1 GROUP BY value
) AS t2 ON (t1.value = t2.value)
ORDER BY t1.Id

或者

SELECT t1.id,t1.value,COUNT(t2.id) AS cnt FROM Table1 AS t1
INNER JOIN Table1 AS t2
   ON  t1.value = t2.value
GROUP BY t1.id,t1.value
ORDER BY t1.id