如何选择 DISTINCT * [英] How to SELECT DISTINCT *
问题描述
这是一个可能的查询吗?
Is this a possible query?
目前,我的数据库中的每个产品都列在我网站的主页上,而且由于一个产品可以属于多个类别,因此其中很多都是重复的.
Currently, every product from my database is being listed on the home page of my website and a lot of them are duplicates since a product can belong to multiple categories.
我正在使用 "SELECT * FROM Books WHERE product_status = '1'";
推荐答案
然后使用 group by 和 max.
Then use group by and max.
select column1, column2, max(category)
from Books
WHERE product_status = '1'
group by column1, column2;
在这个例子中,column1 和 column2 是你在 Books 表中的列(比如 book_title、book_author 或类似的东西......),你可以选择 max(category) 所以只选择一个类别......
In this example column1 and column2 are your columns from table Boooks (like book_title, book_author or something similar...) and you can select max(category) so only one category is selected....
这是小DEMO
在此演示中,仅选择了两本书中的一本.未选择 ID 为 4 的图书,因为它的 product_status = '0'.
In this demo only one of two same books is selected. Book with ID 4 is not selected because it has product_status = '0'.
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