连接表并用指定值替换空值

Question

我正在尝试制作一个可打印的页面，其中包含指定制造商的所有销售，列出指定日期之间的所有产品。如果没有任何销售，则应显示 0。

桌子

// Manufacturer table
// mid, manufacturer
// Products table
// pid, product, ref_manufacturer_id
// Orders table
// oid, orderPrice, orderDateTime, ref_product_id

以及有效的查询（没有日期限制）

SELECT prod.product, COALESCE(COUNT(pord.oid),0) AS orderCount,
COALESCE(SUM(pord.orderPrice),0) AS orderSum
FROM product_manufacturer AS manu
JOIN product_list AS prod ON prod.ref_manufacturer_id = manu.mid
LEFT JOIN product_orders AS pord ON pord.ref_product_id = prod.pid
WHERE manu.mid = :manu_id
GROUP BY prod.product;

但是一旦我添加到 WHERE 语法中

WHERE manu.mid = :manu_id AND DATE(pord.orderDateTime) BETWEEN :orders_start AND :orders_end

我正在使用 PHP PDO 进行连接并验证 manu_id 是否为 int 并且 orders_start/end 已转换为 MySQL 日期格式。

但我想找出的问题是，是什么导致了问题，当我添加日期限制时，每个未订购的产品都不会显示在输出中？

关于创建表的 SQL

CREATE TABLE product_list (
  pid bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  product varchar(255) NOT NULL,
  ref_manufacturer_id bigint(20) unsigned NOT NULL,
  PRIMARY KEY (pid),
  KEY ref_manufacturer_id (ref_manufacturer_id)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;

CREATE TABLE product_manufacturer (
  mid bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  manufacturer varchar(255) NOT NULL,
  PRIMARY KEY (mid),
  UNIQUE KEY manufacturer (manufacturer)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;

CREATE TABLE product_orders (
  oid bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  orderPrice float(10,2) NOT NULL,
  orderDatetime timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  red_product_id bigint(20) unsigned NOT NULL,
  PRIMARY KEY (oid),
  KEY red_product_id (red_product_id)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;

Answer 1

您需要将 orderDateTime 条件移动到连接子句而不是 where 子句，例如：

SELECT prod.product, COALESCE(COUNT(pord.oid),0) AS orderCount,
       COALESCE(SUM(pord.orderPrice),0) AS orderSum
FROM product_manufacturer AS manu
JOIN product_list AS prod ON prod.ref_manufacturer_id = manu.mid
LEFT JOIN product_orders AS pord 
          ON pord.ref_product_id = prod.pid
          AND DATE(pord.orderDateTime) BETWEEN :orders_start AND :orders_end
WHERE manu.mid = :manu_id
GROUP BY prod.product;

它在WHERE 子句中不起作用的原因是从外部连接返回的NULL 值。当您在产品的product_orders 中没有行时，外部联接会为日期字段orderDateTime 返回NULL，并且该行将被过滤掉，因为NULL 不等于任何内容。

Answer 2

试试：

SELECT p.product, 
    COALESCE(o.orderCount, 0) as orderCount, 
    COALESCE(o.orderSum,0) AS orderSum
FROM product_manufacturer AS m
JOIN product_list AS p ON p.ref_manufacturer_id = m.mid
LEFT JOIN (
    SELECT ref_product_id as pid, COUNT(oid) AS orderCount, SUM(orderPrice) AS orderSum
    FROM product_orders
    WHERE DATE(orderDateTime) BETWEEN :orders_start AND :orders_end
    GROUP BY ref_product_id
) AS o ON p.pid = o.pid
WHERE m.mid = :manu_id

编辑：在 ypercube 评论后更正。

Answer 3

在 where 子句上试试这个。

WHERE manu.mid = :manu_id AND (DATE(pord.orderDateTime) BETWEEN :orders_start AND :orders_end)

它可能将第二个 AND 函数作为另一个 where 子句读取，该语句应该返回 true。只是预感而已。让我知道这是否有效。

Answer 4

我不知道您的特定系统是如何工作的，但在订购该产品之前，可能没有设置orderDateTime（即NULL 或其他内容）。你可以试试：

WHERE manu.mid = :manu_id AND ((DATE(pord.orderDateTime) BETWEEN :orders_start AND :orders_end) OR pord.orderDateTime=NULL)

如果不是这样，您能否举一个 orderDateTime 值的示例，说明您希望它不会显示的东西？