我有三个表 - 用户,城市和地区。有趣的选择mysql
users - u_id, u_city
cities - c_id, r_c_id
regions - r_id, r_alias
凡users
和cities
通过r_c_id = r_id
占用由u_city = c_id
和cities
和regions
。我有地区表的r_alias。是否有可能计算我选择的该地区的用户数(我有r_alias)(COUNT(u_id)
)。
感谢您的帮助!
我有三个表 - 用户,城市和地区。有趣的选择mysql
users - u_id, u_city
cities - c_id, r_c_id
regions - r_id, r_alias
凡users
和cities
通过r_c_id = r_id
占用由u_city = c_id
和cities
和regions
。我有地区表的r_alias。是否有可能计算我选择的该地区的用户数(我有r_alias)(COUNT(u_id)
)。
感谢您的帮助!
试试这个:
select count(u_id)
from users
join cities on u_city = c_id
join regions on r_c_id = r_id
where r_alias = "r_alias_value'
是的,这是可能的。
您需要先加入的表,
SELECT a.r_alias, COUNT(*) AS TotalUser
FROM regions a
INNER JOIN cities b
ON a.r_id = b.r_c_id
GROUP BY a.r_alias
这将列出所有区域的用户的具体数量。如果要计算指定的区域,只需添加WHERE
子句。
SELECT a.r_alias, COUNT(*) AS TotalUser
FROM regions a
INNER JOIN cities b
ON a.r_id = b.r_c_id
WHERE a.r_alias = 'valHERE'
GROUP BY a.r_alias
这将是相当更有效率接近
SELECT STRAIGHT_JOIN
r.*,
COUNT(u.u_id) AS `users`
FROM (
SELECT * FROM regions
WHERE r_alias LIKE '$region_alias'
) AS r
LEFT OUTER JOIN cities AS c ON (r.r_id = c.r_c_id)
LEFT OUTER JOIN users AS u ON (u.u_city = c.c_id)
GROUP BY r.r_id;
执行select语句,因为它加入其余表之前筛选到一个特定的区域。
(代码是在MySQL 5.6.10测试)
只是为了纠正你的术语 - 当你说“占用”你意味着“有一个外键关系”(u_city作为外键全市C_ID首要的关键) – Patashu