如何在关系 SQL 查询中使用 NOT

Question

当我这样 select table 时：select count(*) from products 是 returning 12900 结果。

我有一个关系查询 return 多个 table 关系结果如下：

SELECT category.name, 
       manifacturer.name,
       supplier.name,
       product.name
FROM   products as product,
       suppliers as supplier, 
       manifacturers as manifacturer,
       categories as category
WHERE  product.sid=supplier.id AND
       product.manid = manifacturer.id AND
       product.catid = category.id

本次查询returns 12873 结果，

所以我找不到哪个数据不匹配。我怎样才能找到这些丢失的数据？我使用 NOT 查询但没有 return 任何结果。

Answer 1

首先，您应该学会使用正确、明确的 join 语法：

SELECT category.name, manifacturer.name, supplier.name, product.name
FROM   products as product join
       suppliers as supplier
       on product.sid = supplier.id join
       manifacturers as manifacturer
       on product.manid = manifacturer.id join
       categories as category
       on product.catid = category.id;

然后，如果您想要不匹配项，请切换到 left join 并在 where 子句中查找不匹配项：

SELECT category.name, manifacturer.name, supplier.name, product.name
FROM   products as product left join
       suppliers as supplier
       on product.sid = supplier.id left join
       manifacturers as manifacturer
       on product.manid = manifacturer.id left join
       categories as category
       on product.catid = category.id
WHERE supplier.id IS NULL OR manifacturer.id IS NULL or category.id IS NULL;

Answer 2

以下查询 returns 其产品不在您的查询中的记录：

SELECT *
FROM Products P
WHERE (P.sid,P.mainid,P.catid) NOT IN (
    SELECT DISTINCT product.sid
    ,product.mainid
    ,product.catid
    FROM products AS product
        ,suppliers AS supplier
        ,manifacturers AS manifacturer
        ,categories AS category
    WHERE product.sid = supplier.id
        AND product.manid = manifacturer.id
        AND product.catid = category.id
    )

Answer 3

您可以看到不匹配的记录与 FULL OUTER JOIN 是这样的：

SELECT prod.id, rel.id FROM (
SELECT category.name, 
       manifacturer.name,
       supplier.name,
       product.name
FROM   products as product,
       suppliers as supplier, 
       manifacturers as manifacturer,
       categories as category
WHERE  product.sid=supplier.id AND
       product.manid = manifacturer.id AND
       product.catid = category.id
) as rel
FULL OUTER JOIN products as prod
ON rel.id = prod.id

因此您可以在列表中看到 null id 而不是 null id。

Answer 4

除了我上面关于别名的评论之外，您还应该使用 ANSI-92 中引入的 "newer" 连接语法。请注意这里用于同一事物的代码少了多少。您编写代码的方式所有连接都是内部连接，因为您想要 return 行没有匹配我将它们更改为左连接。

SELECT c.name, 
       m.name,
       s.name,
       p.name
FROM products p
left join suppliers s on p.sid = s.id
left join manifacturers m on p.manid = m.id
left join categories c on p.catid = c.id

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