MySQL查詢：錯誤說子查詢返回超過1行

Question

我正在嘗試從兩個表中進行復雜的查詢...這是技能測驗中的一個問題。

表

**Orders                                    Customer**s
    id                                         id
    date                                     first_name
    shipping_amount                          last_name 
    order_status                             city
    customer_id (Customers.id)             state 

產量

-----------+------------+
| State     |  # Orders  |
+-----------+------------+
| NY        |  55        |
| CA        |  40        |
| NJ        |  33        |
| FL        |  21        |
| MO        |  12        |
+-----------+------------+

我一直在進行查詢，看起來像這樣...

select DISTINCT state, (select count(id) Orders
                        from customers
                        group by state
                        ORDER BY Orders DESC) FROM Customers

它給我一個錯誤，表明子查詢返回多於1行

Answer 1

嘗試這個：

SELECT c.state, COUNT(o.id) AS Orders 
FROM Customers c, Orders o 
WHERE o.customer_id = c.id 
GROUP BY state 
ORDER BY Orders DESC

子查詢不是必需的。

Answer 2

SELECT `Customers`.`state`, count(`Orders`.`id`) 
as `orders FROM `Customers` 
LEFT JOIN `Orders` ON `Customers`.`id` = `Orders`.`customer_id` 
GROUP BY `Customers`.`state` 
ORDER BY `orders` DESC

Answer 3

嘗試這個：

select DISTINCT state, (select count(id) as cnt, Orders from customers group by
    state ORDER BY Orders DESC) Temp FROM Customers

Answer 4

SELECT c.state as State, COUNT(o.id) as NumOrders
FROM orders o
LEFT JOIN customers c ON (c.id = o.customer_id)
GROUP BY c.state