SELECT 
  COUNT(*) 
FROM 
  `cscart_company_reviews` 
WHERE 
  `company_id` = 692

Query time 0.00042

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "0.35"
    },
    "table": {
      "table_name": "cscart_company_reviews",
      "access_type": "ALL",
      "rows_examined_per_scan": 1,
      "rows_produced_per_join": 1,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "0.25",
        "eval_cost": "0.10",
        "prefix_cost": "0.35",
        "data_read_per_join": "32"
      },
      "used_columns": [
        "company_id"
      ],
      "attached_condition": "(`dev2`.`cscart_company_reviews`.`company_id` = 692)"
    }
  }
}