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 = 286 
WHERE 
  cscart_products_categories.product_id IN (
    6843, 6840, 6841, 6846, 13274, 13286, 
    13280, 13292, 3430, 3429, 3437, 3436, 
    3438, 3477, 3452, 3478, 3479, 3453, 
    3491, 3488, 3497, 3495, 3489, 3492, 
    3496, 3490, 3494, 6951, 3502, 3503, 
    3493, 3498, 3428, 12850, 12869, 12802
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00341

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "60.79"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "1.48"
      },
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_categories",
            "access_type": "ALL",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "rows_examined_per_scan": 46,
            "rows_produced_per_join": 1,
            "filtered": "4.00",
            "cost_info": {
              "read_cost": "5.15",
              "eval_cost": "0.18",
              "prefix_cost": "5.33",
              "data_read_per_join": "7K"
            },
            "used_columns": [
              "category_id",
              "storefront_id",
              "usergroup_ids",
              "status"
            ],
            "attached_condition": "((`test2_gaseus`.`cscart_categories`.`storefront_id` in (0,1)) and ((`test2_gaseus`.`cscart_categories`.`usergroup_ids` = '') or (0 <> find_in_set(0,`test2_gaseus`.`cscart_categories`.`usergroup_ids`)) or (0 <> find_in_set(1,`test2_gaseus`.`cscart_categories`.`usergroup_ids`))) and (`test2_gaseus`.`cscart_categories`.`status` in ('A','H')))"
          }
        },
        {
          "table": {
            "table_name": "cscart_products_categories",
            "access_type": "ref",
            "possible_keys": [
              "PRIMARY",
              "pt"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id"
            ],
            "key_length": "3",
            "ref": [
              "test2_gaseus.cscart_categories.category_id"
            ],
            "rows_examined_per_scan": 83,
            "rows_produced_per_join": 1,
            "filtered": "0.97",
            "index_condition": "(`test2_gaseus`.`cscart_products_categories`.`product_id` in (6843,6840,6841,6846,13274,13286,13280,13292,3430,3429,3437,3436,3438,3477,3452,3478,3479,3453,3491,3488,3497,3495,3489,3492,3496,3490,3494,6951,3502,3503,3493,3498,3428,12850,12869,12802))",
            "cost_info": {
              "read_cost": "38.18",
              "eval_cost": "0.15",
              "prefix_cost": "58.78",
              "data_read_per_join": "23"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ]
          }
        },
        {
          "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",
              "test2_gaseus.cscart_products_categories.product_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 1,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "0.37",
              "eval_cost": "0.15",
              "prefix_cost": "59.30",
              "data_read_per_join": "23"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        }
      ]
    }
  }
}