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 = 271 
WHERE 
  cscart_products_categories.product_id IN (
    3940, 3941, 3942, 3943, 3944, 3945, 3946, 
    3985, 3986, 3987, 3988, 3989, 3990, 
    3991, 4045, 4046, 4047, 4048, 4049, 
    4050, 4051, 4128, 4129, 4130, 4131, 
    4132, 4133, 4134, 4181, 4182, 4183, 
    4184, 4185, 4186, 4187, 26, 27, 28, 72, 
    73, 74, 75, 133, 134, 135, 136, 137, 138, 
    139, 240, 241, 242, 293, 294, 295, 296, 
    3520, 3521, 3522, 3523, 3524, 3936, 
    3937, 3938, 3983, 3984, 4042, 4043, 
    4044, 4124, 4125, 4126, 4127, 4178, 
    4179, 4180, 43, 44, 45, 46, 47, 48, 49, 
    90, 91, 92, 93, 94, 95, 96, 154, 155, 156, 
    157, 158, 159
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00299

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "68.37"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "1.53"
      },
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_categories",
            "access_type": "ALL",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "rows_examined_per_scan": 40,
            "rows_produced_per_join": 1,
            "filtered": "4.00",
            "cost_info": {
              "read_cost": "4.54",
              "eval_cost": "0.16",
              "prefix_cost": "4.70",
              "data_read_per_join": "6K"
            },
            "used_columns": [
              "category_id",
              "storefront_id",
              "usergroup_ids",
              "status"
            ],
            "attached_condition": "((`gaseus`.`cscart_categories`.`storefront_id` in (0,1)) and ((`gaseus`.`cscart_categories`.`usergroup_ids` = '') or (0 <> find_in_set(0,`gaseus`.`cscart_categories`.`usergroup_ids`)) or (0 <> find_in_set(1,`gaseus`.`cscart_categories`.`usergroup_ids`))) and (`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": [
              "gaseus.cscart_categories.category_id"
            ],
            "rows_examined_per_scan": 110,
            "rows_produced_per_join": 1,
            "filtered": "0.87",
            "index_condition": "(`gaseus`.`cscart_products_categories`.`product_id` in (3940,3941,3942,3943,3944,3945,3946,3985,3986,3987,3988,3989,3990,3991,4045,4046,4047,4048,4049,4050,4051,4128,4129,4130,4131,4132,4133,4134,4181,4182,4183,4184,4185,4186,4187,26,27,28,72,73,74,75,133,134,135,136,137,138,139,240,241,242,293,294,295,296,3520,3521,3522,3523,3524,3936,3937,3938,3983,3984,4042,4043,4044,4124,4125,4126,4127,4178,4179,4180,43,44,45,46,47,48,49,90,91,92,93,94,95,96,154,155,156,157,158,159))",
            "cost_info": {
              "read_cost": "44.00",
              "eval_cost": "0.15",
              "prefix_cost": "66.30",
              "data_read_per_join": "24"
            },
            "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",
              "gaseus.cscart_products_categories.product_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 1,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "0.38",
              "eval_cost": "0.15",
              "prefix_cost": "66.84",
              "data_read_per_join": "24"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        }
      ]
    }
  }
}