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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 = 103598 
  AND object_type = 'U'

Query time 0.00038

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "21.43"
    },
    "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": 38,
          "rows_produced_per_join": 38,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "4.33",
            "eval_cost": "3.80",
            "prefix_cost": "8.13",
            "data_read_per_join": "29K"
          },
          "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": 38,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "9.50",
            "eval_cost": "3.80",
            "prefix_cost": "21.43",
            "data_read_per_join": "38K"
          },
          "used_columns": [
            "field_id",
            "field_type"
          ]
        }
      }
    ]
  }
}

Result

field_id	value	field_type
51	1	S
53	5	S
54	32	K
54	33	K
54	90	K
55	54	S
56	19	K
56	20	K
56	21	K
56	23	K
56	56	K
56	57	K
56	58	K
68		I
72	74	S
81	100	S
82	103	K
84	106	K
84	107	K
85	109	K
85	110	K
86	112	K
86	114	K
86	115	K
88	124	K
88	129	K
88	130	K
89	131	K
89	133	K
89	134	K
89	135	K
89	137	K
89	138	K
90	144	S
91	147	S
92	151	S
93	154	S
95	161	S

field_id	value	field_type
51	1	S
53	5	S
54	32	K
54	33	K
54	90	K
55	54	S
56	19	K
56	20	K
56	21	K
56	23	K
56	56	K
56	57	K
56	58	K
68		I
72	74	S
81	100	S
82	103	K
84	106	K
84	107	K
85	109	K
85	110	K
86	112	K
86	114	K
86	115	K
88	124	K
88	129	K
88	130	K
89	131	K
89	133	K
89	134	K
89	135	K
89	137	K
89	138	K
90	144	S
91	147	S
92	151	S
93	154	S
95	161	S

field_id	value	field_type
51	1	S
53	5	S
54	32	K
54	33	K
54	90	K
55	54	S
56	19	K
56	20	K
56	21	K
56	23	K
56	56	K
56	57	K
56	58	K
68		I
72	74	S
81	100	S
82	103	K
84	106	K
84	107	K
85	109	K
85	110	K
86	112	K
86	114	K
86	115	K
88	124	K
88	129	K
88	130	K
89	131	K
89	133	K
89	134	K
89	135	K
89	137	K
89	138	K
90	144	S
91	147	S
92	151	S
93	154	S
95	161	S

field_id	value	field_type
51	1	S
53	5	S
54	32	K
54	33	K
54	90	K
55	54	S
56	19	K
56	20	K
56	21	K
56	23	K
56	56	K
56	57	K
56	58	K
68		I
72	74	S
81	100	S
82	103	K
84	106	K
84	107	K
85	109	K
85	110	K
86	112	K
86	114	K
86	115	K
88	124	K
88	129	K
88	130	K
89	131	K
89	133	K
89	134	K
89	135	K
89	137	K
89	138	K
90	144	S
91	147	S
92	151	S
93	154	S
95	161	S