php - MySQL/PHP 从多个表中选择和计数

Question

我什至不确定这是可能的......我会告诉你我正在做什么，然后我想做什么:

状态:

state_id

城镇:

town_id
state_id
misc_property

街道:

street_id
town_id
state_id

这些是按层次结构设置的。

我要选择的内容:

我想选择所有具有 misc_property 的城镇，同时选择它所属的州并计算该城镇的所有街道。

这是我目前所拥有的:

$sql="SELECT 
    a.state_id AS state_id, 
    b.town_id AS town_id, 
    COUNT(c.street_id) 

    FROM 
    state a, 
    town b, 
    street c 

    WHERE 
    b.misc_property='$property'";

Answer 1

使用这个查询:

SELECT
    town.state_id AS state_id,
    town.town_id AS town_id,
    COUNT(street.street_id) AS count
FROM
    state INNER JOIN town ON state.state_id = town.state_id 
    LEFT JOIN street ON town.town_id = street.town_id
GROUP BY
    state_id,
    town_id
HAVING
    town.misc_property = 'stuff';