的MySQL/PHP選擇並從多個表

Question

計數我什至不知道這是可能的...我會告訴你什麼是我的工作，我想怎樣做：

狀態：

state_id 

鎮：

town_id 
state_id 
misc_property 

街道：

street_id 
town_id 
state_id 

這些設置在一個層次結構中。

我想選擇什麼：

我想選擇所有城鎮以及misc_property，而在選擇的狀態，同時它屬於計數所有的街道在該城。

這是我到目前爲止有：

$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

使用此查詢：

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'; 

Answer 2

您可以使用GROUP BY town_id有對特殊WHERE條件

Answer 3

使用聯接：

SELECT * FROM state 
LEFT JOIN town ON state.state_id = town.state_id 
LEFT JOIN street ON street.town_id = town.town_id 
WHERE town.misc_property = '$property' 

Answer 4

你可以這樣做

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

    FROM 
    state a, 
    town b, 
    street c 

    WHERE 
    b.misc_property='$property'and b.state_id = a.state_id "