SELECT 
  * 
FROM 
  cscart_ec_spin_rules 
WHERE 
  product_id = 278

Query time 0.00026

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "20.20"
    },
    "table": {
      "table_name": "cscart_ec_spin_rules",
      "access_type": "ALL",
      "rows_examined_per_scan": 96,
      "rows_produced_per_join": 9,
      "filtered": "10.00",
      "cost_info": {
        "read_cost": "18.28",
        "eval_cost": "1.92",
        "prefix_cost": "20.20",
        "data_read_per_join": "384"
      },
      "used_columns": [
        "rule_id",
        "product_id",
        "discount_type",
        "discount_value",
        "ec_spin_segment_color",
        "probability",
        "status"
      ],
      "attached_condition": "(`rajansecarter_15_june_mve`.`cscart_ec_spin_rules`.`product_id` = 278)"
    }
  }
}