Question

鉴于此查询：

SELECT `promotions`.* 
FROM `promotions` 
    INNER JOIN `orders_promotions` ON `promotions`.`id` = `orders_promotions`.`promotion_id` 
WHERE `orders_promotions`.`order_id` = 3
AND `promotions`.`code` = 'blablabla'

我想知道最后一个WHERE（WHERE `promotions`.`code` = 'blablabla'）语句是针对WHOLE promotions表，还是针对INNER JOIN返回的集合？

Answer 1

执行SQL查询的操作顺序如下所示

FROM clause
JOIN clause
WHERE clause
GROUP BY clause
HAVING clause
SELECT clause
ORDER BY clause

正如您在WHERE操作执行后看到JOIN所见;这表示在上面发布的查询中WHERE条件将对从JOIN操作获得的结果集起作用。

您可以更改查询并在JOIN ON子句中包含条件，以便在它到达WHERE子句之前进行过滤，如

SELECT `promotions`.* 
FROM `promotions` 
INNER JOIN `orders_promotions` 
ON `promotions`.`id` = `orders_promotions`.`promotion_id` 
AND `orders_promotions`.`order_id` = 3
WHERE `promotions`.`code` = 'blablabla'

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INNER JOIN的Where子句 - 子集或原始表上的行为？

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