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 = 54 
WHERE 
  cscart_products_categories.product_id IN (
    18516, 51007, 51004, 51005, 51010, 51008, 
    51012, 51013, 51011, 51015, 51006, 
    51021, 51016, 51024, 51017, 51019, 
    51018, 51022, 51014, 51045, 51422, 
    51025, 51440, 51424, 51029, 51442, 
    51429, 51060, 51436, 51430, 51433, 
    51027, 51063, 51020, 51067, 51423, 
    51431, 51435, 51028, 51031, 51062, 
    51042, 51441, 51432, 51434, 51030, 
    51032, 51033, 51425, 51026, 51035, 
    51059, 51069, 51070, 51038, 51066, 
    51023, 51041, 51056, 51040, 51050, 
    51065, 51039, 51052
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00285

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "97.66"
    },
    "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": 71,
            "rows_produced_per_join": 71,
            "filtered": "100.00",
            "index_condition": "(`test_uchur_k`.`cscart_products_categories`.`product_id` in (18516,51007,51004,51005,51010,51008,51012,51013,51011,51015,51006,51021,51016,51024,51017,51019,51018,51022,51014,51045,51422,51025,51440,51424,51029,51442,51429,51060,51436,51430,51433,51027,51063,51020,51067,51423,51431,51435,51028,51031,51062,51042,51441,51432,51434,51030,51032,51033,51425,51026,51035,51059,51069,51070,51038,51066,51023,51041,51056,51040,51050,51065,51039,51052))",
            "cost_info": {
              "read_cost": "40.86",
              "eval_cost": "7.10",
              "prefix_cost": "47.96",
              "data_read_per_join": "1K"
            },
            "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",
              "test_uchur_k.cscart_products_categories.product_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 71,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "17.75",
              "eval_cost": "7.10",
              "prefix_cost": "72.81",
              "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": [
              "test_uchur_k.cscart_products_categories.category_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 3,
            "filtered": "5.00",
            "cost_info": {
              "read_cost": "17.75",
              "eval_cost": "0.36",
              "prefix_cost": "97.66",
              "data_read_per_join": "18K"
            },
            "used_columns": [
              "category_id",
              "storefront_id",
              "usergroup_ids",
              "status"
            ],
            "attached_condition": "((`test_uchur_k`.`cscart_categories`.`storefront_id` in (0,1)) and ((`test_uchur_k`.`cscart_categories`.`usergroup_ids` = '') or (0 <> find_in_set(0,`test_uchur_k`.`cscart_categories`.`usergroup_ids`)) or (0 <> find_in_set(1,`test_uchur_k`.`cscart_categories`.`usergroup_ids`))) and (`test_uchur_k`.`cscart_categories`.`status` in ('A','H')))"
          }
        }
      ]
    }
  }
}