mysql - 计数类似记录的数量、平均计数和具有特定计数的 #

Question

我有一个带有非唯一名称字段的 MySql 表，我想查询以下内容；

对于每个名称值（“John”）计算有多少条记录（名称为 John 的 32 条记录），我最终会将其写入每条记录。

平均每个名称组的计数（例如，John 的 32 条记录和 Sally 的 42 条记录，表 37 记录的平均值）

计数意味着例如 6 个 10 记录组、10 个 20 记录组等

我可以通过一个或多个查询来做到这一点吗？

Answer 1

表组的平均值http://sqlfiddle.com/#!2/f5af3/5：

SELECT 
  AVG(ct) 
FROM (
  SELECT 
    COUNT(name) as ct 
  FROM 
    names 
  GROUP BY  
    name) as temp1;

按计数计数http://sqlfiddle.com/#!2/b0628/1：

SELECT 
  COUNT(ct) AS "Count_per_count",
  ct as "Actual Count" 
FROM (
  SELECT 
    COUNT(name) as ct 
  FROM 
    names 
  GROUP BY 
    name) as temp1 
GROUP BY ct;

Answer 2

select name, count(*) as num from table group by name;

select ((select count(*) from table) / (select count(distinct name) from table));

select count(*) as num, type from
    (select count(*) as type from table group by name) t
group by type