Mysql从两个表中选择没有关系

Question

I have two tables first one has PRODUCTS_ID and second table has the relation between products for example product 1 has relation with product (2,3,4,5) as shown in PRODUCT_CONN . What I need to get the products listed on Table 1 that has no relation to product 1 then the result should be like that "6,7,8".

TABLE 1
========
PRODUCTS_ID
    1   
    2   
    3   
    4
    5
    6
    7
    8   

TABLE2
======
PRODUCT_ID  | PRODUCT_CONN
    1       |   2
    1       |   3
    1       |   4
    1       |   5

Answer 1

One way you can do this, is joining both tables, and then filtering the rows for discard those that have relations with product ID 1 , like in next example:

SELECT
    TABLE_1.PRODUCTS_ID
FROM
   TABLE_1
LEFT JOIN
   TABLE_2 ON TABLE_2.PRODUCT_CONN = TABLE_1.PRODUCTS_ID
WHERE
   TABLE_1.PRODUCTS_ID <> 1
AND
   (TABLE_2.PRODUCT_ID IS NULL OR TABLE_2.PRODUCT_ID <> 1)

Alternatively, you could first select all IDs that are connected to product with ID 1 , and then select all IDs that are not in this set, excluding also product ID 1 , like this:

SELECT
    PRODUCTS_ID
FROM
    TABLE_1
WHERE
    PRODUCTS_ID NOT IN (SELECT PRODUCT_CONN
                        FROM TABLE_2
                        WHERE PRODUCT_ID = 1)
AND
    PRODUCTS_ID <> 1;