SELECT 
  product_review_id 
FROM 
  cscart_product_reviews 
  LEFT JOIN cscart_users ON cscart_product_reviews.reply_user_id = cscart_users.user_id 
  LEFT JOIN cscart_companies ON cscart_users.company_id = cscart_companies.company_id 
  LEFT JOIN cscart_country_descriptions ON cscart_product_reviews.country_code = cscart_country_descriptions.code 
  AND cscart_country_descriptions.lang_code = 'en' 
WHERE 
  1 
  AND cscart_product_reviews.product_id IN (68916) 
  AND cscart_product_reviews.status = 'A' 
GROUP BY 
  cscart_product_reviews.product_review_id

Query time 0.00920

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "16.94"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_product_reviews",
            "access_type": "index_merge",
            "possible_keys": [
              "PRIMARY",
              "idx_product_id",
              "idx_user_id",
              "idx_product_reviews_status"
            ],
            "key": "intersect(idx_product_id,idx_product_reviews_status)",
            "key_length": "3,3",
            "rows_examined_per_scan": 5,
            "rows_produced_per_join": 5,
            "filtered": "90.91",
            "cost_info": {
              "read_cost": "7.54",
              "eval_cost": "0.50",
              "prefix_cost": "8.04",
              "data_read_per_join": "8K"
            },
            "used_columns": [
              "product_review_id",
              "product_id",
              "country_code",
              "reply_user_id",
              "status"
            ],
            "attached_condition": "((`cscart_db`.`cscart_product_reviews`.`product_id` = 68916) and (`cscart_db`.`cscart_product_reviews`.`status` = 'A'))"
          }
        },
        {
          "table": {
            "table_name": "cscart_users",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "user_id"
            ],
            "key_length": "3",
            "ref": [
              "cscart_db.cscart_product_reviews.reply_user_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 5,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "4.91",
              "eval_cost": "0.50",
              "prefix_cost": "13.45",
              "data_read_per_join": "35K"
            },
            "used_columns": [
              "user_id",
              "company_id"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_companies",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "company_id"
            ],
            "key_length": "4",
            "ref": [
              "cscart_db.cscart_users.company_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 5,
            "filtered": "100.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "1.25",
              "eval_cost": "0.50",
              "prefix_cost": "15.20",
              "data_read_per_join": "34K"
            },
            "used_columns": [
              "company_id"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_country_descriptions",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "code",
              "lang_code"
            ],
            "key_length": "12",
            "ref": [
              "cscart_db.cscart_product_reviews.country_code",
              "const"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 5,
            "filtered": "100.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "1.25",
              "eval_cost": "0.50",
              "prefix_cost": "16.95",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "code",
              "lang_code"
            ]
          }
        }
      ]
    }
  }
}