SELECT 
  category_id 
FROM 
  cscart_categories 
WHERE 
  category_id IN('198', '199', '197') 
  AND ec_enable_rfq = 'Y'

Query time 0.00037

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "7.21"
    },
    "table": {
      "table_name": "cscart_categories",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "p_category_id"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "category_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 3,
      "rows_produced_per_join": 0,
      "filtered": "10.00",
      "index_condition": "(`atulecarter_atul_demo7`.`cscart_categories`.`category_id` in ('198','199','197'))",
      "cost_info": {
        "read_cost": "7.15",
        "eval_cost": "0.06",
        "prefix_cost": "7.21",
        "data_read_per_join": "801"
      },
      "used_columns": [
        "category_id",
        "ec_enable_rfq"
      ],
      "attached_condition": "(`atulecarter_atul_demo7`.`cscart_categories`.`ec_enable_rfq` = 'Y')"
    }
  }
}