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 (
    265000, 40404, 262379, 265262, 392209, 
    339537, 114747, 271509, 339493, 265255, 
    339524, 339540, 339536, 339491, 265241, 
    114761, 265230, 339517, 339522, 339526, 
    339520, 285971, 81644, 265236, 81606, 
    81700, 271508, 265251, 271499, 224457, 
    271501, 339490, 392218, 265238, 265240, 
    392216, 265253, 392217, 81601, 366896, 
    339741, 381654, 265243, 265264, 81687, 
    339498, 271507, 339449, 265233, 32880, 
    339528, 224454, 381657, 81703, 391799, 
    265234, 265257, 381658, 339497, 339689, 
    224455, 265259, 285967, 81679, 339448, 
    265249, 265252, 339450, 265260, 359820, 
    339435, 392151, 265239, 285969, 381656, 
    339622, 339442, 381655, 81666, 339616, 
    339443, 152086, 339436, 170242, 339574, 
    259708, 339523, 339507, 205875, 339437, 
    339504, 339451, 339512, 265035, 81683, 
    139611, 339740, 339609, 339500, 339532
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00466

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "289.56"
    },
    "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": 103,
            "rows_produced_per_join": 103,
            "filtered": "100.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "21.76",
              "eval_cost": "20.60",
              "prefix_cost": "42.36",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ],
            "attached_condition": "(`webmarco`.`cscart_products_categories`.`product_id` in (265000,40404,262379,265262,392209,339537,114747,271509,339493,265255,339524,339540,339536,339491,265241,114761,265230,339517,339522,339526,339520,285971,81644,265236,81606,81700,271508,265251,271499,224457,271501,339490,392218,265238,265240,392216,265253,392217,81601,366896,339741,381654,265243,265264,81687,339498,271507,339449,265233,32880,339528,224454,381657,81703,391799,265234,265257,381658,339497,339689,224455,265259,285967,81679,339448,265249,265252,339450,265260,359820,339435,392151,265239,285969,381656,339622,339442,381655,81666,339616,339443,152086,339436,170242,339574,259708,339523,339507,205875,339437,339504,339451,339512,265035,81683,139611,339740,339609,339500,339532))"
          }
        },
        {
          "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": 103,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "103.00",
              "eval_cost": "20.60",
              "prefix_cost": "165.96",
              "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": "103.00",
              "eval_cost": "1.03",
              "prefix_cost": "289.56",
              "data_read_per_join": "30K"
            },
            "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')))"
          }
        }
      ]
    }
  }
}