MySQL Group By 并根据条件从分组结果中返回不同的行

Question

Background

1. The table below shows the list of products across the three branches of a particular Phone Shop
2. "branch_id" with value "0" means the product is available in all branches
3. I would like to query for distinct products whose "branch_id = 2" - including those in a comma-separated string AND "branch_id = 0";
4. However, if the result returns more than one row with the same "product_name", in this case "Iphone X", the row with the "branch_id" not equal to "0" should be returned.

Products

id	product_name	branch_id	price
1	Iphone X	2,3	700
2	Iphone X	0	500
3	Samsung S8	2	600
4	Ipad Pro	1	750
5	Apple watch	0	550
6	Samsung S9	1,2	600

Expected Result

id	product_name	branch_id	price
1	Iphone X	2	700
3	Samsung S8	2	600
5	Apple watch	0	550
6	Samsung S9	2	600

My Query - it doesn't return rows with branch_id = 0

    select  id, product_name, branch_id, price FROM products 
    group by product_name,branch_id 
    having CASE 
       WHEN FIND_IN_SET(2, branch_id) > 0 THEN FIND_IN_SET(2, branch_id) > 0
       WHEN branch_id = 0 THEN branch_id = 0
       ELSE  branch_id = NULL 
    END

Answer 1

Use NOT EXISTS :

SELECT id, product_name, 
       CASE WHEN branch_id = '0' THEN branch_id ELSE '2' END branch_id, 
       price
FROM Products p1
WHERE FIND_IN_SET(2, p1.branch_id)
   OR (
     p1.branch_id = 0 
     AND NOT EXISTS (
       SELECT 1
       FROM Products p2
       WHERE p2.product_name = p1.product_name
         AND FIND_IN_SET(2, p2.branch_id)
     )
   );

Or, if your version of MySql is 8.0+ use ROW_NUMBER() window function:

SELECT id, product_name, 
       CASE WHEN branch_id = '0' THEN branch_id ELSE '2' END branch_id, 
       price
FROM (
  SELECT *, ROW_NUMBER() OVER (PARTITION BY product_name ORDER BY FIND_IN_SET(2, branch_id) > 0 DESC) rn
  FROM Products
  WHERE FIND_IN_SET(2, branch_id) OR branch_id = '0'
) t
WHERE rn = 1

See the demo .