如何在同一条select语句中使用count和group by

我有一个分组的SQL选择查询。我想对group by语句之后的所有记录进行计数。有没有办法直接从SQL？例如，有一个包含用户的表格，我想选择不同的城镇和用户总数

select town, count(*) from user
group by town

我想有一列包含所有城镇，另一列包含所有行中的用户数。

共有3个镇和58个用户的结果示例是：

Town         Count
Copenhagen   58
NewYork      58
Athens       58

这将完成您想要的操作（城镇列表以及每个城镇中的用户数量）：

select town, count(town) 
from user
group by town

使用时，您可以使用大多数聚合函数GROUP BY。

更新（对问题和评论进行更改之后）

您可以为用户数量声明一个变量，并将其设置为用户数量，然后选择该变量。

DECLARE @numOfUsers INT
SET @numOfUsers = SELECT COUNT(*) FROM user

SELECT DISTINCT town, @numOfUsers
FROM user

您可以使用COUNT(DISTINCT ...)：

SELECT COUNT(DISTINCT town) 
FROM user

另一种方法是：

/* Number of rows in a derived table called d1. */
select count(*) from
(
  /* Number of times each town appears in user. */
  select town, count(*)
  from user
  group by town
) d1

使用Oracle，您可以使用分析功能：

select town, count(town), sum(count(town)) over () total_count from user
group by town

您的其他选择是使用子查询：

select town, count(town), (select count(town) from user) as total_count from user
group by town

如果您想按计数排序（听起来很简单，但我找不到如何做到这一点的答案），可以这样做：

        SELECT town, count(town) as total FROM user
        GROUP BY town ORDER BY total DESC

十个未删除的答案；大多数人不会按照用户的要求进行操作。大多数答案误以为是每个城镇有58位用户，而不是总共58位用户。即使是少数正确的方法也不是最优的。

mysql> flush status;
Query OK, 0 rows affected (0.00 sec)

SELECT  province, total_cities
    FROM       ( SELECT  DISTINCT province  FROM  canada ) AS provinces
    CROSS JOIN ( SELECT  COUNT(*) total_cities  FROM  canada ) AS tot;
+---------------------------+--------------+
| province                  | total_cities |
+---------------------------+--------------+
| Alberta                   |         5484 |
| British Columbia          |         5484 |
| Manitoba                  |         5484 |
| New Brunswick             |         5484 |
| Newfoundland and Labrador |         5484 |
| Northwest Territories     |         5484 |
| Nova Scotia               |         5484 |
| Nunavut                   |         5484 |
| Ontario                   |         5484 |
| Prince Edward Island      |         5484 |
| Quebec                    |         5484 |
| Saskatchewan              |         5484 |
| Yukon                     |         5484 |
+---------------------------+--------------+
13 rows in set (0.01 sec)

SHOW session status LIKE 'Handler%';

+----------------------------+-------+
| Variable_name              | Value |
+----------------------------+-------+
| Handler_commit             | 1     |
| Handler_delete             | 0     |
| Handler_discover           | 0     |
| Handler_external_lock      | 4     |
| Handler_mrr_init           | 0     |
| Handler_prepare            | 0     |
| Handler_read_first         | 3     |
| Handler_read_key           | 16    |
| Handler_read_last          | 1     |
| Handler_read_next          | 5484  |  -- One table scan to get COUNT(*)
| Handler_read_prev          | 0     |
| Handler_read_rnd           | 0     |
| Handler_read_rnd_next      | 15    |
| Handler_rollback           | 0     |
| Handler_savepoint          | 0     |
| Handler_savepoint_rollback | 0     |
| Handler_update             | 0     |
| Handler_write              | 14    |  -- leapfrog through index to find provinces  
+----------------------------+-------+

在OP的上下文中：

SELECT  town, total_users
    FROM       ( SELECT  DISTINCT town  FROM  canada ) AS towns
    CROSS JOIN ( SELECT  COUNT(*) total_users  FROM  canada ) AS tot;

由于距离只有一排tot，因此CROSS JOIN不会像其他地方那样庞大。

通常的模式是COUNT(*)代替COUNT(town)。后者意味着检查是否town为空，这在此上下文中是不必要的。

您可以像milkovovsky所说的那样在COUNT内部使用DISTINCT

就我而言：

select COUNT(distinct user_id) from answers_votes where answer_id in (694,695);

这将拉取被认为与user_id相同的答案投票数

我知道这是SQL Server中的旧帖子：

select  isnull(town,'TOTAL') Town, count(*) cnt
from    user
group by town WITH ROLLUP

Town         cnt
Copenhagen   58
NewYork      58
Athens       58
TOTAL        174

如果要选择镇和用户总数，则可以在下面使用此查询：

SELECT Town, (SELECT Count(*) FROM User) `Count` FROM user GROUP BY Town;

如果要使用“选择所有带计数的查询”选项，请尝试此操作...

 select a.*, (Select count(b.name) from table_name as b where Condition) as totCount from table_name  as a where where Condition

尝试以下代码：

select ccode, count(empno) 
from company_details 
group by ccode;