PHP mysql插入不工作没有错误检查

Question

我的表有2个字段，主要是自动增量，然后是entry_id

为什么下面没有插入表中：

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

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

$entry_id = 5;

$sql = "INSERT INTO orders (entry_id) VALUE ('$entry_id')";


$conn->close();
?>

但是在添加错误时会检查它吗？

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

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

$entry_id = 5;

$sql = "INSERT INTO orders (entry_id) VALUE ('$entry_id')";
if ($conn->query($sql) === TRUE) {
    echo "";
} else {
    echo "Error: " . $sql . "<br>" . $conn->error;
}

$conn->close();
?>

无法理解为什么会发生这种情况。