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 (
    6417, 6416, 5607, 5605, 5606, 5699, 5703, 
    5701, 5700, 5697, 5702, 5698, 7249, 
    7247, 7243, 7248, 7246, 7244, 7242, 
    7245, 6692, 6702, 6703, 6704, 6705, 
    6707, 6708, 6706, 5704, 1294, 1297, 
    1301, 1298, 1299, 1300, 1296, 1295, 
    3576, 3585, 3584, 3575, 7601, 7602, 
    6709, 3146, 3752, 3145, 5096
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00350

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "181.23"
    },
    "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": 207,
            "rows_produced_per_join": 207,
            "filtered": "100.00",
            "index_condition": "(`dbggbern`.`cscart_products_categories`.`product_id` in (6417,6416,5607,5605,5606,5699,5703,5701,5700,5697,5702,5698,7249,7247,7243,7248,7246,7244,7242,7245,6692,6702,6703,6704,6705,6707,6708,6706,5704,1294,1297,1301,1298,1299,1300,1296,1295,3576,3585,3584,3575,7601,7602,6709,3146,3752,3145,5096))",
            "cost_info": {
              "read_cost": "84.46",
              "eval_cost": "20.70",
              "prefix_cost": "105.16",
              "data_read_per_join": "3K"
            },
            "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": 10,
            "filtered": "5.00",
            "cost_info": {
              "read_cost": "51.75",
              "eval_cost": "1.04",
              "prefix_cost": "177.61",
              "data_read_per_join": "41K"
            },
            "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": 10,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "2.59",
              "eval_cost": "1.04",
              "prefix_cost": "181.23",
              "data_read_per_join": "165"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        }
      ]
    }
  }
}