Question

我有以下查询：

    SELECT DISTINCT id, title
    FROM      
    ((SELECT 
        DISTINCT offers.id AS id, offers.title AS title

    FROM offers

    INNER JOIN categories
    ON offers.category=categories.title

    WHERE categories.title="Fashion clothes"

    GROUP BY offers.id
    ORDER BY offers.id)
    UNION ALL
    (SELECT 
        DISTINCT offers.id AS id, offers.title AS title

    FROM offers

    INNER JOIN cities
    ON offers.city=cities.title

    WHERE cities.title="Australia"

    GROUP BY offers.id
    ORDER BY offers.id)) as subquery

我想从表中提取包含category=Fashion衣服和city=Australia的行，但是当我使用Union时，它会返回所有行。我不知道如何让它发挥作用。如果有人可以帮助我会很感激。

Answer 1

你不需要工会。只需加入所有表，并在where where子句中包含两个条件：

SELECT 
DISTINCT offers.id AS id, offers.title AS title

FROM offers
INNER JOIN categories
ON offers.category=categories.title
INNER JOIN cities
ON offers.city=cities.title

WHERE categories.title="Fashion clothes" AND cities.title="Australia"
ORDER BY offers.id

正如RubahMalam所指出的那样，当您按标题加入表时，您甚至不需要连接，因此查询可以简化为：

SELECT 
DISTINCT offers.id AS id, offers.title AS title

FROM offers

WHERE offers.category="Fashion clothes" AND offers.city="Australia"
ORDER BY offers.id

但是，最好在所有表格中使用单独的唯一ID，并使用这些ID在您的查询中加入它们，但这是另一个故事。

Answer 2

你只需要：

SELECT id,title
FROM offers
WHERE category = "Fashion clothes" OR city = "Australia"
GROUP BY id,title
ORDER BY offers.id

您甚至不需要INNER JOIN。正如patrickh003所说，如果id是唯一列，则甚至不需要GROUP BY。

Answer 3

如果你想要两者，那么你可以使用聚合和拥有子句：

SELECT o.id, o.title
FROM offers o
WHERE o.category = 'Fashion clothes' AND o.city = 'Australia'
GROUP BY o.id, o.title
HAVING COUNT(*) = 2
ORDER BY o.id;

如果您可以在offers表格中包含重复项，那么您需要COUNT(DISTINCT o.category)子句中的HAVING而不是COUNT(*)。

将两个不同的查询合并为一个

3 个答案: