php的独特限制

这是我使用的脚本

<?php
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "merlin";
$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}    
$time_start = microtime(true);
$sql = "SELECT Distinct host_name FROM report_data limit 5";
$time_end = microtime(true);
if ($conn->query($sql) === TRUE) {
echo "Job Done ";
} else {
echo "Error: " . $sql . "<br>" . $conn->error;
}   
$time = $time_end - $time_start;
echo "In $time seconds\n";       
$conn->close();
?>     

输出：

错误：从报告数据限制5中选择不同的主机名称 在0秒内

    <?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

$sql = "SELECT Distinct host_name FROM report_data limit 5";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    // output data of each row
    while($row = $result->fetch_assoc()) {
        echo "host_name: " . $row["host_name"]. "<br>";
    }
} else {
    echo "0 results";
}
$conn->close();
?> 

---

mysqli:：query

不会返回

true

，这是您的全部问题。查询工作正常。对于

SELECT

查询，它将返回一个结果集，我想您可能希望循环使用该结果集。请阅读此功能的手册：

是否检查了数据库连接？出现了什么错误？你的完整代码是什么。请，在你需要添加更多信息时投入一些精力：发布脚本和你得到的错误，效果非常好！谢谢

if ($conn->query($sql) === TRUE) ..