SELECT 
  filter_id 
FROM 
  cscart_product_filters 
WHERE 
  mdc_code = 'mdc_models'

Query time 0.00031

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "24.62"
    },
    "table": {
      "table_name": "cscart_product_filters",
      "access_type": "ALL",
      "rows_examined_per_scan": 107,
      "rows_produced_per_join": 10,
      "filtered": "10.00",
      "cost_info": {
        "read_cost": "22.48",
        "eval_cost": "2.14",
        "prefix_cost": "24.62",
        "data_read_per_join": "8K"
      },
      "used_columns": [
        "filter_id",
        "mdc_code"
      ],
      "attached_condition": "(`danishecarter_25_march`.`cscart_product_filters`.`mdc_code` = 'mdc_models')"
    }
  }
}