SELECT 
  * 
FROM 
  `cscart_gr__sf_names` 
WHERE 
  `category_id` = 702

Query time 0.00023

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "0.78"
    },
    "table": {
      "table_name": "cscart_gr__sf_names",
      "access_type": "ref",
      "possible_keys": [
        "category_id"
      ],
      "key": "category_id",
      "used_key_parts": [
        "category_id"
      ],
      "key_length": "4",
      "ref": [
        "const"
      ],
      "rows_examined_per_scan": 1,
      "rows_produced_per_join": 1,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "0.68",
        "eval_cost": "0.10",
        "prefix_cost": "0.78",
        "data_read_per_join": "344"
      },
      "used_columns": [
        "sf_id",
        "category_id",
        "features_hash",
        "fixed",
        "company_id",
        "show_in_breadcrumbs",
        "relink",
        "relink_blog"
      ]
    }
  }
}