php - php 中 num_rows() 的 mysql 行数可靠吗？

Question

我在 php 中使用 mysqli_num_rows() 来计算查询行数，然后在 Docs 中使用我读到:

The behaviour of mysqli_num_rows() depends on whether buffered or unbuffered result sets are being used. For unbuffered result sets, mysqli_num_rows() will not return the correct number of rows until all the rows in the result have been retrieved

它们到底是什么意思？查询何时无缓冲以及何时缓冲？

谢谢。

Answer 1

示例

返回结果集中的行数:

<?php
$con=mysqli_connect("localhost","my_user","my_password","my_db");

检查连接

if (mysqli_connect_errno())
  {
   echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }

$sql="SELECT Lastname,Age FROM Persons ORDER BY Lastname";

if ($result=mysqli_query($con,$sql))
  {

返回结果集中的行数

$rowcount=mysqli_num_rows($result);
  printf("Result set has %d rows.\n",$rowcount);

免费结果集

  mysqli_free_result($result);
  }
 mysqli_close($con);
?>