SELECT 
  ushop_profile_field_descriptions.cp_maxlength, 
  ushop_profile_field_descriptions.cp_placeholder, 
  ushop_profile_field_descriptions.cp_prompt 
FROM 
  ushop_profile_field_descriptions 
  LEFT JOIN ushop_profile_fields ON ushop_profile_fields.field_id = ushop_profile_field_descriptions.object_id 
WHERE 
  ushop_profile_fields.field_name = 'email' 
  AND ushop_profile_fields.profile_type = 'U'

Query time 0.00094

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "5.04"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "ushop_profile_fields",
          "access_type": "ref",
          "possible_keys": [
            "PRIMARY",
            "field_name"
          ],
          "key": "field_name",
          "used_key_parts": [
            "field_name"
          ],
          "key_length": "98",
          "ref": [
            "const"
          ],
          "rows_examined_per_scan": 12,
          "rows_produced_per_join": 1,
          "filtered": "10.00",
          "cost_info": {
            "read_cost": "3.00",
            "eval_cost": "0.12",
            "prefix_cost": "4.20",
            "data_read_per_join": "1K"
          },
          "used_columns": [
            "field_id",
            "field_name",
            "profile_type"
          ],
          "attached_condition": "((`marketplace`.`ushop_profile_fields`.`profile_type` = 'U') and (`marketplace`.`ushop_profile_fields`.`field_id` is not null))"
        }
      },
      {
        "table": {
          "table_name": "ushop_profile_field_descriptions",
          "access_type": "ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "object_id"
          ],
          "key_length": "3",
          "ref": [
            "marketplace.ushop_profile_fields.field_id"
          ],
          "rows_examined_per_scan": 2,
          "rows_produced_per_join": 2,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "0.60",
            "eval_cost": "0.24",
            "prefix_cost": "5.04",
            "data_read_per_join": "5K"
          },
          "used_columns": [
            "object_id",
            "cp_maxlength",
            "cp_placeholder",
            "cp_prompt"
          ]
        }
      }
    ]
  }
}