关于sql：如何在同一个select语句中使用count和group by

How to use count and group by at the same select statement

我有一个SQL选择查询，它有一个分组依据。我想计算group by语句之后的所有记录。有没有直接从SQL实现的方法？例如，如果有一个包含用户的表，我想选择不同的城镇和用户总数

1 2	SELECT town, COUNT(*) FROM USER GROUP BY town

我想要一个包含所有城镇的列，另一个包含所有行中的用户数。

有3个镇和58个用户的结果示例如下：

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Town COUNT
Copenhagen 58
NewYork 58
Athens 58

号

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这将满足您的需求(城镇列表，以及每个城镇的用户数)：

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SELECT town, COUNT(town)
FROM USER
GROUP BY town

使用GROUP BY时，可以使用大多数聚合函数。

更新(更改问题和评论后)

您可以为用户数声明一个变量，并将其设置为用户数，然后使用该变量进行选择。

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

SELECT DISTINCT town, @numOfUsers
FROM USER

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您可以使用COUNT(DISTINCT ...)：

1 2	SELECT COUNT(DISTINCT town) FROM USER

。

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另一种方法是：

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/* 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

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如果您想按计数排序(听起来很简单，但我在如何排序的堆栈上找不到答案)，可以执行以下操作：

1 2	SELECT town, COUNT(town) AS total FROM USER GROUP BY town ORDER BY total DESC

。

使用Oracle，您可以使用分析功能：

1 2	SELECT town, COUNT(town), SUM(COUNT(town)) OVER () total_count FROM USER GROUP BY town

您的其他选项是使用子查询：

1 2	SELECT town, COUNT(town), (SELECT COUNT(town) FROM USER) AS total_count FROM USER GROUP BY town

。

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我知道这是一篇老文章，在SQL Server中：

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SELECT isnull(town,'TOTAL') Town, COUNT(*) cnt
FROM USER
GROUP BY town WITH ROLLUP

Town cnt
Copenhagen 58
NewYork 58
Athens 58
TOTAL 174

。

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你可以像米尔科夫斯基所说的那样在伯爵内部使用独特的

就我而言：

1	SELECT COUNT(DISTINCT user_id) FROM answers_votes WHERE answer_id IN (694,695);

这将拉取与一个计数相同的用户ID的应答投票计数。

十个未删除的答案；大多数不做用户要求的。大多数回答错误地理解了这个问题，认为每个城镇有58个用户，而不是总共58个。即使是少数正确的也不是最佳的。

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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)

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埃多克斯1〔2〕

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+----------------------------+-------+
| 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
+----------------------------+-------+

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在操作环境中：

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

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由于tot只有一行，因此CROSS JOIN的体积并不像其他的那样大。

通常的模式是COUNT(*)，而不是COUNT(town)。后者意味着检查town是否不为空，这在本文中是不必要的。

如果要选择"城镇"和"用户总数"，可以使用下面的查询：

1	SELECT Town, (SELECT COUNT(*) FROM USER) `Count` FROM USER GROUP BY Town;

。

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如果要使用Select all query with count选项，请尝试此操作…

1	SELECT a.*, (SELECT COUNT(b.name) FROM TABLE_NAME AS b WHERE Condition) AS totCount FROM TABLE_NAME AS a WHERE WHERE Condition

号

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尝试以下代码：

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SELECT ccode, COUNT(empno)
FROM company_details
GROUP BY ccode;

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