从同一类别中选择多个产品？

Question

声明尝试1：

似乎忽略了一切，无论来自哪个国家/地区，都能获得产品

SELECT *
FROM products
WHERE `country` = 'America' AND
      product = 'Product 1' AND
      product = 'Product 2' AND
      completed = 'complete'

声明尝试2：

这样做的结果是返回0个结果，即使结果假设在那里。

SELECT *
FROM products
WHERE `country` = 'America' AND
      product = 'Product 1' OR
      product = 'Product 2' AND
      completed = 'complete'

Answer 1

由于product = product 1 AND product = product 2，您的第一个查询在逻辑上是不正确的，其中子句逐行过滤，因此同一行不能同时在product列中包含两个值。

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您的第二个查询存在一个您引入的问题和OR条件，因此如果产品2在另一个国家/地区完成状态，则它会忽略国家/地区过滤条件，要更正您的查询，您需要按以下方式对OR条件进行分组使用括号(condition 1 or condition 2) and some other condition

SELECT *
FROM products
WHERE `country` = 'America'
      AND (product = 'Product 1' OR product = 'Product 2')
      AND completed = 'complete'

或者您可以使用IN子句简化条件

SELECT *
FROM products
WHERE `country` = 'America'
      AND product IN('Product 1','Product 2')
      AND completed = 'complete'