搜索多个表的mysql

Question

I have a table Product and Classification and a join table Product_Classification. I wrote a query to search through the tables. One thing I notice is that If I have a product record (or Classification) that is not mapped to Classification the query will not return anything. How can I change my query in a such a way that it does ALSO return a Product that is not mapped a Classification (and a Classification data that is not mapped to a product).

$query = "Select *   from $dbname.Product P INNER JOIN Product_Classification PC ON P.ProductID = PC.ProductID INNER JOIN Classification C ON PC.ClassificationID = C.ClassificationID ";

EDIT: I do have a Where condition, which is an array of fields

Answer 1

You can use this query

$query = "Select *   from $dbname.Product P LEFT JOIN Product_Classification PC ON P.ProductID = PC.ProductID LEFT JOIN Classification C ON PC.ClassificationID = C.ClassificationID ";

If you want to see more about joins, this link will help you https://stackoverflow.com/a/4715847/6098214

Answer 2

使用此查询

Select *   from $dbname.Product P INNER JOIN Product_Classification PC ON P.ProductID = PC.ProductID LEFT JOIN Classification C ON PC.ClassificationID = C.ClassificationID