SELECT 
  cscart_products_categories.product_id, 
  GROUP_CONCAT(
    IF(
      cscart_products_categories.link_type = "M", 
      CONCAT(
        cscart_products_categories.category_id, 
        "M"
      ), 
      cscart_products_categories.category_id
    )
  ) AS category_ids, 
  product_position_source.position AS position 
FROM 
  cscart_products_categories 
  INNER JOIN cscart_categories ON cscart_categories.category_id = cscart_products_categories.category_id 
  AND cscart_categories.storefront_id IN (0, 1) 
  AND (
    cscart_categories.usergroup_ids = '' 
    OR FIND_IN_SET(
      0, cscart_categories.usergroup_ids
    ) 
    OR FIND_IN_SET(
      1, cscart_categories.usergroup_ids
    )
  ) 
  AND cscart_categories.status IN ('A', 'H') 
  LEFT JOIN cscart_products_categories AS product_position_source ON cscart_products_categories.product_id = product_position_source.product_id 
  AND product_position_source.category_id = 9 
WHERE 
  cscart_products_categories.product_id IN (
    4341, 4342, 6036, 4347, 6369, 4344, 4345, 
    5303, 6050, 7351, 5304, 4348, 4346, 
    6349, 6345, 4122, 2743, 3544, 3545, 
    3543, 3541, 3540, 4956, 5114, 2645, 
    7301, 7299, 7300, 2646, 2647, 2644, 
    1410, 5154, 5150, 5153, 2648, 5152, 
    5155, 5151, 2886, 6436, 2773, 6440, 
    7223, 7116, 7221, 7222, 7224
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00341

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "155.07"
    },
    "grouping_operation": {
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_products_categories",
            "access_type": "range",
            "possible_keys": [
              "PRIMARY",
              "pt"
            ],
            "key": "pt",
            "used_key_parts": [
              "product_id"
            ],
            "key_length": "3",
            "rows_examined_per_scan": 175,
            "rows_produced_per_join": 175,
            "filtered": "100.00",
            "index_condition": "(`dbggbern`.`cscart_products_categories`.`product_id` in (4341,4342,6036,4347,6369,4344,4345,5303,6050,7351,5304,4348,4346,6349,6345,4122,2743,3544,3545,3543,3541,3540,4956,5114,2645,7301,7299,7300,2646,2647,2644,1410,5154,5150,5153,2648,5152,5155,5151,2886,6436,2773,6440,7223,7116,7221,7222,7224))",
            "cost_info": {
              "read_cost": "73.26",
              "eval_cost": "17.50",
              "prefix_cost": "90.76",
              "data_read_per_join": "2K"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_categories",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id"
            ],
            "key_length": "3",
            "ref": [
              "dbggbern.cscart_products_categories.category_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 8,
            "filtered": "5.00",
            "cost_info": {
              "read_cost": "43.75",
              "eval_cost": "0.88",
              "prefix_cost": "152.01",
              "data_read_per_join": "35K"
            },
            "used_columns": [
              "category_id",
              "usergroup_ids",
              "status",
              "storefront_id"
            ],
            "attached_condition": "((`dbggbern`.`cscart_categories`.`storefront_id` in (0,1)) and ((`dbggbern`.`cscart_categories`.`usergroup_ids` = '') or (0 <> find_in_set(0,`dbggbern`.`cscart_categories`.`usergroup_ids`)) or (0 <> find_in_set(1,`dbggbern`.`cscart_categories`.`usergroup_ids`))) and (`dbggbern`.`cscart_categories`.`status` in ('A','H')))"
          }
        },
        {
          "table": {
            "table_name": "product_position_source",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "pt"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id",
              "product_id"
            ],
            "key_length": "6",
            "ref": [
              "const",
              "dbggbern.cscart_products_categories.product_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 8,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "2.19",
              "eval_cost": "0.88",
              "prefix_cost": "155.07",
              "data_read_per_join": "140"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        }
      ]
    }
  }
}