SELECT 
  profile_fields_data.field_id, 
  profile_fields_data.value, 
  profile_fields.field_type 
FROM 
  cscart_profile_fields_data AS profile_fields_data 
  LEFT JOIN cscart_profile_fields AS profile_fields ON profile_fields_data.field_id = profile_fields.field_id 
WHERE 
  object_id = 87939 
  AND object_type = 'U'

Query time 0.00042

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "30.10"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "profile_fields_data",
          "access_type": "ref",
          "possible_keys": [
            "idx_entire_row",
            "idx_obj_objtyp"
          ],
          "key": "idx_obj_objtyp",
          "used_key_parts": [
            "object_id",
            "object_type"
          ],
          "key_length": "6",
          "ref": [
            "const",
            "const"
          ],
          "rows_examined_per_scan": 54,
          "rows_produced_per_join": 54,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "5.80",
            "eval_cost": "5.40",
            "prefix_cost": "11.20",
            "data_read_per_join": "41K"
          },
          "used_columns": [
            "object_id",
            "object_type",
            "field_id",
            "value"
          ]
        }
      },
      {
        "table": {
          "table_name": "profile_fields",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "field_id"
          ],
          "key_length": "3",
          "ref": [
            "cscart_db.profile_fields_data.field_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 54,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "13.50",
            "eval_cost": "5.40",
            "prefix_cost": "30.10",
            "data_read_per_join": "55K"
          },
          "used_columns": [
            "field_id",
            "field_type"
          ]
        }
      }
    ]
  }
}

Result

field_id value field_type
51 2 S
53 4 S
54 32 K
54 33 K
54 37 K
54 90 K
54 91 K
55 54 S
56 18 K
56 19 K
56 20 K
56 21 K
56 23 K
56 56 K
56 58 K
68 I
70 64 K
70 67 K
72 74 S
80 95 K
80 97 K
81 99 S
82 102 K
82 103 K
82 104 K
82 105 K
84 106 K
84 107 K
84 108 K
85 109 K
86 112 K
86 113 K
87 121 S
88 123 K
88 124 K
88 125 K
88 126 K
88 128 K
88 130 K
89 131 K
89 132 K
89 134 K
89 135 K
89 137 K
90 143 S
91 148 S
92 150 S
93 154 S
95 160 S
98 165 K
98 168 K
99 172 S
101 178 S
103 27 I