mysql_free_result() only needs to be called when considering how much memory it will take up when returning a very large result set. All associated memory will be automatically released after the script ends.

After we execute the SELECT statement, it is a good habit to release the cursor memory. . Memory release can be achieved through the PHP function mysql_free_result().

//定義頭文件，字符格式
 header("Content-type:text/html;charset=utf-8");
 error_reporting(ERR_ALL & ~ E_NOTICE);
 
 //定義本地服務(wù)器連接信息
 $servername="localhost";
 $username="root";
 $password="admin";
 $dbname="test";
 
 //本地連接
 $conn=mysqli_connect($servername,$username,$password,$dbname)or die(mysqli_error());
 
//要查詢的信息
$sql="SELECT firstname,lastname,email FROM hello";
$result=mysqli_query($conn,$sql);
 
//判斷字符串是否執(zhí)行成功
if($result){
 while($row=mysqli_fetch_array($result,MYSQLI_ASSOC))  {
    echo $row["firstname"]." ".$row["lastname"]." ".$row["email"]."<br>";
    echo "<hr>";
  }
}else{
  die("fetch data failed!");
}
 
//釋放游標(biāo)內(nèi)存
mysqli_free_result($result);
//關(guān)閉數(shù)據(jù)庫連接
mysqli_close($conn);

Note: In addition to talking about mysqli_free_result, I also want to mention the second parameter of the mysqli_fetch_array() function

mysqli_fetch_array(result,resulttype)
resulttype parameter:
1: MYSQLI_ASSOC, the returned result array is associated Array, the key of the array is the corresponding field name, you can use it like this:
row['firstname'], row['lastname']...

2: MYSQLI_NUM, the returned result array is the index array, The keys of the array are numeric indexes such as 0,1,2,3,4. You can only use it like this:
$row[0], row[1]...

3: MYSQLI_BOTH, the returned result array There are both field indexes and numeric indexes in . When you use it, both of the above can be used.