无法通过PHP查询MySQL数据库

在我的PHP代码中,我很容易将记录写入我的数据库,但由于某种原因,我无法读取任何信息.我的PHP代码是:

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

$sql = "SELECT * FROM companies";

if ($conn->query($sql) === TRUE)
{
    echo "query success";

    while($row = $result->fetch_assoc())
    {
        echo "ID: " . $row["ID"]. " - Name: " . $row["name"]. "
";
    }
}
else
{
    echo "query failure";
    echo "Error: " . $sql . "
" . $conn->error;
}


$sql = "INSERT INTO companies (name) 
        VALUES ('mycompany')";

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

    echo "insert success";
}
else
{
    echo "insert failure";
    echo "Error: " . $sql . "
" . $conn->error;
}

我运行它时从浏览器获得的输出是: query failureError: SELECT * FROM companies insert success

我已尝试过撇号,插入符号,$ sql字符串中的引号.我试过在HeidiSQL中运行这个查询,它运行正常.我出错的任何想法？有什么更基本的建议我可以尝试缩小问题的根源吗？

谢谢!

使用mysqli->query()with SELECT语句返回的实例mysqli_result.它与true(=== true)不同,但也不代表错误.

而且,$result未定义.

请改用:

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

$sql = "SELECT * FROM companies";

if (($result = $conn->query($sql)) !== FALSE)
{
    echo "query success";

    while($row = $result->fetch_assoc())
    {
        echo "ID: " . $row["ID"]. " - Name: " . $row["name"]. "
";
    }
}
else
{
    echo "query failure";
    echo "Error: " . $sql . "
" . $conn->error;
}
...

这只是将您的=== TRUE支票更改为!== FALSE.MySQLi::query()在失败时返回布尔值FALSE,对于没有结果集的成功查询或者结果集成功后返回布尔值TRUE mysqli_result.这也将query()的结果分配给$result.