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 (
    339678, 431132, 265042, 339796, 339541, 
    339477, 339457, 339700, 431202, 431162, 
    339811, 339489, 339458, 431128, 431099, 
    339623, 431155, 392172, 339453, 339797, 
    339606, 339798, 339699, 430639, 431141, 
    339643, 339469, 392167, 431130, 431168, 
    339482, 339685, 431153, 339730, 431154, 
    339731, 431137, 431096, 339463, 381703, 
    392175, 339709, 431124, 339460, 430637, 
    431125, 381725, 339478, 339468, 431094, 
    339467, 430745, 431146, 339810, 430911, 
    339753, 431134, 430640, 431048, 339696, 
    431033, 431187, 339806, 339805, 339757, 
    339794, 339701, 339808, 431191, 430697, 
    430767, 431067, 431117, 339464, 339787, 
    381701, 431157, 431104, 381687, 431090, 
    392166, 431107, 431116, 431204, 339452, 
    431196, 431065, 339752, 339814, 430744, 
    431084, 339695, 339750, 431203, 431176, 
    339656, 431100, 431199, 430655, 431160
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00279

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 (339678,431132,265042,339796,339541,339477,339457,339700,431202,431162,339811,339489,339458,431128,431099,339623,431155,392172,339453,339797,339606,339798,339699,430639,431141,339643,339469,392167,431130,431168,339482,339685,431153,339730,431154,339731,431137,431096,339463,381703,392175,339709,431124,339460,430637,431125,381725,339478,339468,431094,339467,430745,431146,339810,430911,339753,431134,430640,431048,339696,431033,431187,339806,339805,339757,339794,339701,339808,431191,430697,430767,431067,431117,339464,339787,381701,431157,431104,381687,431090,392166,431107,431116,431204,339452,431196,431065,339752,339814,430744,431084,339695,339750,431203,431176,339656,431100,431199,430655,431160))"
          }
        },
        {
          "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')))"
          }
        }
      ]
    }
  }
}