SELECT 
  sf_id 
FROM 
  cscart_gr__sf_names n 
WHERE 
  n.category_id = 740 
  AND (
    LENGTH(n.features_hash)= 9 
    AND LOCATE('461-14350', n.features_hash)> 0 
    AND n.fixed in ('F', 'U')
  ) 
  AND n.show_in_breadcrumbs = 'Y'

Query time 0.00027

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "1.01"
    },
    "table": {
      "table_name": "n",
      "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": 0,
      "filtered": "5.00",
      "cost_info": {
        "read_cost": "0.91",
        "eval_cost": "0.01",
        "prefix_cost": "1.01",
        "data_read_per_join": "17"
      },
      "used_columns": [
        "sf_id",
        "category_id",
        "features_hash",
        "fixed",
        "show_in_breadcrumbs"
      ],
      "attached_condition": "((length(`dev2`.`n`.`features_hash`) = 9) and (locate('461-14350',`dev2`.`n`.`features_hash`) > 0) and (`dev2`.`n`.`fixed` in ('F','U')) and (`dev2`.`n`.`show_in_breadcrumbs` = 'Y'))"
    }
  }
}