Question

我有这个查询

SELECT 
    (SELECT keyword FROM url_aliAS WHERE query = CONCAT("category_id" , '=', p2c.category_id)) AS something,
    p.product_id, p.model FROM product AS p 
    JOIN product_to_category p2c ON (p.product_id = p2c.product_id)  
        WHERE p.product_id NOT IN (280, 129, 131)

并且返回的行具有重复的product_id。例如： -

something       product_id  model
NULL            20         18924
barcode_labels  20         18924
NULL            21         18926
barcode_labels  21         18926
NULL            22         30332
barcode_labels  22         30332

我在DISTINCT上尝试了product_id，我也尝试了WHERE子句“并且某些内容不为空”并且都失败了。有解决方案吗？

Answer 1

你可能想要这样的东西（我也稍微重构了一下代码）。但是，如果您的关键字不仅仅是barcode_labels，那么您仍会为其他组合获得额外的条目。

select
    u.keyword as something,
    product_id,
    p.model
from
    product p
    join product_to_category p2c using (product_id)
    join url_alias u on (u.query = concat("category_id=", p2c.category_id))
where
    u.keyword is not null
    and p.product_id not in (280, 129, 131)

另一种方法是使用group by子句来获得你想要的东西。尝试这样的事情：

select
    max(u.keyword) as something,
    product_id,
    p.model
from
    product p
    join product_to_category p2c using (product_id)
    join url_alias u on (u.query = concat("category_id=", p2c.category_id))
where
    u.keyword is not null
    and p.product_id not in (280, 129, 131)
group by
    product_id,
    p.model

Answer 2

您可以对记录进行分组：

SELECT 
(SELECT keyword FROM url_aliAS WHERE query = CONCAT("category_id" , '=', p2c.category_id)) AS something,
p.product_id, p.model FROM product AS p 
JOIN product_to_category p2c ON (p.product_id = p2c.product_id)  
    WHERE p.product_id NOT IN (280, 129, 131)
GROUP BY p.product_id

但您对分组后显示的信息没有很多控制权。在您的情况下，在某个列中，它应显示NULL还是barcode_labels？

我如何确保此查询没有重复

2 个答案: