php - MySQL 查询在 PHP 中使用时返回空结果，但在 MySQL 客户端中完美运行

Question

我看到还有很多其他类似的帖子涉及类似的问题，但没有一个能解决我的问题。

我有以下 .php 文件:

<?php
$servername = "localhost";
$username = "myusername";
$password = "mypassword";

// Create connection
$conn = mysqli_connect($servername, $username, $password);

// Check connection
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}
echo "Connected successfully";

$sql = "SELECT DISTINCT fase FROM tornei WHERE categoria='18' AND edizione='4' AND anno='2015'";
$result = mysqli_query($conn, $sql);

if (mysqli_num_rows($result) > 0) {
    // output data of each row
    while($row = mysqli_fetch_assoc($result)) {
        echo "fase: " . $row["fase"];
    }
} else {
    echo "0 results";
}

mysqli_close($conn);
?> 

在 MySQL 客户端上执行时，查询正确返回预期结果:

+--------+
| fase   |
+--------+
| gironi |
+--------+

在日志中，我收到以下错误:

PHP Warning:  mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given in /home/admin/domains/domain.com/public_html/query.php on line 18

Answer 1

您尚未将“数据库”名称放入 mysqli_connect 中。正确的语法在这里:

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