mysql - 如何计算联接表上的行数

Question

我有 2 个表 - 一个主（称为组）和详细信息（称为用户）

我想返回每个主行以供后续显示，但我只想计算有多少详细行与主行匹配

我的查询不能正常工作——它只返回主表中的第一行

$query_string = '
    SELECT groups.userGroupID, userGroup,
           count(users.userGroupID) AS howMany
    FROM groups_table AS groups
    JOIN users_table AS users ON users.userGroupID = groups.userGroupID
    ORDER BY groups.userGroupID
';

感谢您的帮助。

Answer 1

通过以下方式忘记您的群组：

SELECT groups.userGroupID, userGroup,
       count(users.userGroupID) AS howMany
FROM groups_table AS groups
LEFT JOIN users_table AS users ON users.userGroupID = groups.userGroupID
GROUP BY groups.userGroupID
ORDER BY groups.userGroupID

Answer 2

这对我有用，希望它可以帮助其他寻找相同答案的人

SELECT COUNT(howMany) AS fo2
FROM(
 SELECT groups.userGroupID, userGroup,
 users.userGroupID AS howMany
 FROM groups_table AS groups
 JOIN users_table AS users ON users.userGroupID = groups.userGroupID
 ORDER BY groups.userGroupID) AS myCount