Question

我需要sql帮助查询：我想创建一个列出商店顾客的视图。这是一个用户表的选择，它已经进行了一次或多次预订（表预订）或已经进行了一次或多次订购（table shop_orders）。

-------------    --------------
| users:    |    | shops:     |
-------------    --------------
| id (PK)   |    | id (PK)    |
-------------    --------------

------------------    ----------------
| reservations:  |    | shops_orders:|
------------------    ----------------
| id (PK)        |    | id (PK)      |
| user_id (FK)   |    | user_id (FK) |
| shop_id (FK)   |    | shop_id (FK) |
------------------    ----------------

这是我的起点，工作正常：

SELECT u.*,
       r.shop_id,
      (SELECT count(*)
       FROM reservations r
       WHERE r.user_id = u.id) AS num_reservations,
      (SELECT count(*)
       FROM shop_orders so
       WHERE so.user_id = u.id) AS num_orders
FROM users u
INNER JOIN (SELECT r.user_id,
                   r.shop_id
            FROM reservations r
            UNION 
            SELECT so.user_id,
                   so.shop_id
            FROM shop_orders so) AS r ON u.id = r.user_id
GROUP BY u.id

此视图的所有查询都将由shop_id过滤，仅显示具体商店的客户（是商店管理区域）。

仅选择有预订或订单的客户（num_reservations＆gt; 0或num_orders＆gt; 0）

我发现的问题是性能：整个表中有2个计数（*）。还有这两个整表之间的联合。

你认为我能测试一种更好的替代方法吗？

Answer 1

你可以这样做：

SELECT 
    u.*,
    r.shop_id,
    IFNULL(COUNT(DISTINCT r.id), 0) AS num_reservations,
    IFNULL(COUNT(DISTINCT o.id), 0) AS num_orders
FROM users u 
    LEFT JOIN reservarions r ON r.user_id = u.id
    LEFT JOIN shop_orders o ON o.user_id = u.id
GROUP BY u.id
HAVING num_reservations + num_orders > 0

另一种方式，应该更快：

SELECT 
    u.*,
    r.shop_id,
    IFNULL(COUNT(DISTINCT r.id), 0) AS num_reservations,
    IFNULL(COUNT(DISTINCT o.id), 0) AS num_orders
FROM users u 
    LEFT JOIN reservarions r ON r.user_id = u.id
    LEFT JOIN shop_orders o ON o.user_id = u.id
WHERE r.id IS NOT NULL OR o.id IS NOT NULL
GROUP BY u.id

如果您需要将用户和商店分开使用，请执行GROUP BY u.id, r.shop_id。

查询列出商店的客户，具有两个不同的订单表

1 个答案: