MySQL选择连接在何处AND

Question

我的数据库中有两个表:

制品

• id(int,主键)
• 名称(varchar)

ProductTags

• product_id(int)
• tag_id(int)

我想选择具有所有给定标签的产品.我试过了:

SELECT
    *
FROM
    Products
JOIN ProductTags ON Products.id = ProductTags.product_id
WHERE
    ProductTags.tag_id IN (1, 2, 3)
GROUP BY
    Products.id

但它给了我带有任何给定标签的产品,而不是所有给定的标签.写作WHERE tag_id = 1 AND tag_id = 2毫无意义,因为不会返回任何行.

Answer 1

这种类型的问题称为关系划分

SELECT Products.* 
FROM Products
JOIN ProductTags ON Products.id = ProductTags.product_id
WHERE ProductTags.tag_id IN (1,2,3)
GROUP BY Products.id /*<--This is OK in MySQL other RDBMSs 
                          would want the whole SELECT list*/

HAVING COUNT(DISTINCT ProductTags.tag_id) = 3 /*Assuming that there is a unique
                                              constraint on product_id,tag_id you 
                                              don't need the DISTINCT*/