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 = 266 
WHERE 
  cscart_products_categories.product_id IN (
    339487, 339682, 339613, 339639, 339555, 
    339480, 339560, 271697, 339579, 339854, 
    339680, 339559, 339788, 339850, 339772, 
    339475, 339815, 339785, 339561, 339566, 
    339766, 339558, 339568, 339688, 339661, 
    339563, 339819, 339837, 339640, 339585, 
    339790, 339598, 339634, 381694, 339578, 
    339546, 339629, 392159, 339672, 381692, 
    339844, 339641, 339624, 339832, 339627, 
    339840, 381689, 339687, 381685, 220162, 
    339842, 339612, 339800, 339642, 339827, 
    265036, 339764, 339605, 339564, 220170, 
    431190, 339690, 339462, 381682, 430574, 
    339562, 339663, 339793, 339554, 339700, 
    271696, 392172, 271695, 431092, 339792, 
    381688, 431106, 435505, 339811, 381693, 
    381691, 220169, 431147, 339801, 339459, 
    339590, 339473, 339592, 430849, 220166, 
    339799, 339679, 381690, 339791, 339795, 
    339660, 339623, 339803, 339813, 339659
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00385

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "281.15"
    },
    "grouping_operation": {
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_products_categories",
            "access_type": "range",
            "possible_keys": [
              "PRIMARY",
              "link_type",
              "pt"
            ],
            "key": "pt",
            "used_key_parts": [
              "product_id"
            ],
            "key_length": "3",
            "rows_examined_per_scan": 100,
            "rows_produced_per_join": 100,
            "filtered": "100.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "21.15",
              "eval_cost": "20.00",
              "prefix_cost": "41.15",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ],
            "attached_condition": "(`webmarco`.`cscart_products_categories`.`product_id` in (339487,339682,339613,339639,339555,339480,339560,271697,339579,339854,339680,339559,339788,339850,339772,339475,339815,339785,339561,339566,339766,339558,339568,339688,339661,339563,339819,339837,339640,339585,339790,339598,339634,381694,339578,339546,339629,392159,339672,381692,339844,339641,339624,339832,339627,339840,381689,339687,381685,220162,339842,339612,339800,339642,339827,265036,339764,339605,339564,220170,431190,339690,339462,381682,430574,339562,339663,339793,339554,339700,271696,392172,271695,431092,339792,381688,431106,435505,339811,381693,381691,220169,431147,339801,339459,339590,339473,339592,430849,220166,339799,339679,381690,339791,339795,339660,339623,339803,339813,339659))"
          }
        },
        {
          "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",
              "webmarco.cscart_products_categories.product_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 100,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "100.00",
              "eval_cost": "20.00",
              "prefix_cost": "161.15",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        },
        {
          "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": [
              "webmarco.cscart_products_categories.category_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 5,
            "filtered": "5.00",
            "cost_info": {
              "read_cost": "100.00",
              "eval_cost": "1.00",
              "prefix_cost": "281.15",
              "data_read_per_join": "29K"
            },
            "used_columns": [
              "category_id",
              "usergroup_ids",
              "status",
              "storefront_id"
            ],
            "attached_condition": "((`webmarco`.`cscart_categories`.`storefront_id` in (0,1)) and ((`webmarco`.`cscart_categories`.`usergroup_ids` = '') or find_in_set(0,`webmarco`.`cscart_categories`.`usergroup_ids`) or find_in_set(1,`webmarco`.`cscart_categories`.`usergroup_ids`)) and (`webmarco`.`cscart_categories`.`status` in ('A','H')))"
          }
        }
      ]
    }
  }
}