SELECT 
  * 
from 
  cscart_product_reviews 
WHERE 
  product_id = '2' 
  AND user_id = '2'

Query time 0.00037

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "0.35"
    },
    "table": {
      "table_name": "cscart_product_reviews",
      "access_type": "ref",
      "possible_keys": [
        "idx_product_id",
        "idx_user_id"
      ],
      "key": "idx_product_id",
      "used_key_parts": [
        "product_id"
      ],
      "key_length": "3",
      "ref": [
        "const"
      ],
      "rows_examined_per_scan": 1,
      "rows_produced_per_join": 0,
      "filtered": "5.00",
      "cost_info": {
        "read_cost": "0.25",
        "eval_cost": "0.01",
        "prefix_cost": "0.35",
        "data_read_per_join": "83"
      },
      "used_columns": [
        "product_review_id",
        "product_id",
        "user_id",
        "name",
        "advantages",
        "disadvantages",
        "comment",
        "rating_value",
        "ip_address",
        "is_buyer",
        "product_review_timestamp",
        "country_code",
        "city",
        "reply_user_id",
        "reply",
        "reply_timestamp",
        "helpfulness",
        "status",
        "storefront_id",
        "images_count",
        "vote_up",
        "vote_down"
      ],
      "attached_condition": "(`cscart_db`.`cscart_product_reviews`.`user_id` = 2)"
    }
  }
}