高级搜索功能-SQL

Question

i'm working on an advanced search functionality on my website. Basically data I'm working on is stored within two tables.

First table contains basic information about the product (1 row = 1 product so it's unique). Table structure may look like this:

id, title, description

The second table contains more information about the product. The product may but don't have to have any rows here. However, one product may store in the second table a few rows. What's more - data in the second table should be used to the advanced search functionality. Table structure may looks like this:

id, item_id (from table 1), value_id (from another table), value

I want to select only these products (table 1) which has specified value_id (from column 2):

... WHERE table1.item_id = 5 AND table2.value_id = 1000

As I mentioned before - table 2 may but doesn't have to contains any rows connected by item_id with the table 1.

I've tried to use JOIN/LEFT JOIN function in SQL but in this case when the product has 3 rows in the table 2 - a query result returns 3 rows instead of 1 or 0 (if not found any results).

How can I handle that?

Answer 1

You want to select products. So select from the product table. You want to select only those for which exists a certain attribute. So create an approriate WHERE clause. As you want to look up data in another table, you could use EXISTS or IN .

select *
from items
where id in (select item_id from item_values where value_id = 1000);