SELECT 
  field_id, 
  value 
FROM 
  q_profile_fields_data 
WHERE 
  object_id = 21 
  AND object_type = 'S'

Query time 0.00169

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "2.40"
    },
    "table": {
      "table_name": "q_profile_fields_data",
      "access_type": "ref",
      "possible_keys": [
        "PRIMARY"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "object_id",
        "object_type"
      ],
      "key_length": "6",
      "ref": [
        "const",
        "const"
      ],
      "rows_examined_per_scan": 2,
      "rows_produced_per_join": 2,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "2.00",
        "eval_cost": "0.40",
        "prefix_cost": "2.40",
        "data_read_per_join": "1K"
      },
      "used_columns": [
        "object_id",
        "object_type",
        "field_id",
        "value"
      ]
    }
  }
}