php mysql null

// 插入数据时明确指定字段的值，即使为NULL
$sql = "INSERT INTO table_name (column1, column2) VALUES (?, ?)";
$stmt = $pdo->prepare($sql);
$stmt->execute([$value1, $value2]); // 如果$value2为null，字段将被设置为NULL

// 使用IS NULL或IS NOT NULL进行条件判断
$sql = "SELECT * FROM table_name WHERE column_name IS NULL";
$results = $pdo->query($sql)->fetchAll();

// 或者在PHP中进行判断
if ($value === null) {
    // 处理NULL值的情况
}

// 使用条件判断来避免设置NULL值
if ($newValue !== null) {
    $sql = "UPDATE table_name SET column_name = ? WHERE id = ?";
    $stmt = $pdo->prepare($sql);
    $stmt->execute([$newValue, $id]);
}

<?php
$pdo = new PDO('mysql:host=localhost;dbname=testdb', 'username', 'password');

// 插入数据
$value1 = 'SomeValue';
$value2 = null; // 允许为NULL
$sql = "INSERT INTO example_table (column1, column2) VALUES (?, ?)";
$stmt = $pdo->prepare($sql);
$stmt->execute([$value1, $value2]);

// 查询数据
$sql = "SELECT * FROM example_table WHERE column2 IS NULL";
$results = $pdo->query($sql)->fetchAll(PDO::FETCH_ASSOC);

foreach ($results as $row) {
    echo "Column1: " . htmlspecialchars($row['column1']) . "<br>";
}
?>