写一个php添加的代码，数据库包含a.id,bookname,categoryName,salePrice,picture,publishingName from books AS a INNER JOIN books_category AS b ON a.categoryId=b.id，图片的值为'upload/'.$newFileName

好的，根据您的描述，我可以提供以下的PHP代码来添加一条数据到books表中：

<?php
// 假设您已经连接到数据库
// 假设您已经获取了表单提交的数据
$bookname = $_POST['bookname'];
$categoryName = $_POST['categoryName'];
$salePrice = $_POST['salePrice'];
$picture = 'upload/'.$newFileName; // 假设$newFileName是您上传的图片文件名
$publishingName = $_POST['publishingName'];

// 准备SQL语句，使用INNER JOIN来关联books和books_category表
$sql = "INSERT INTO books (bookname, categoryId, salePrice, picture, publishingName)
        SELECT :bookname, b.id, :salePrice, :picture, :publishingName
        FROM books_category AS b
        WHERE b.categoryName = :categoryName";

// 准备执行SQL语句的参数
$params = array(
    ':bookname' => $bookname,
    ':categoryName' => $categoryName,
    ':salePrice' => $salePrice,
    ':picture' => $picture,
    ':publishingName' => $publishingName,
);

// 执行SQL语句，并检查是否执行成功
$stmt = $pdo->prepare($sql);
if ($stmt->execute($params)) {
    echo "Add book successfully.";
} else {
    echo "Failed to add book.";
}
?>

上面的代码使用了PDO来执行SQL语句，使用了预处理语句来减少SQL注入的风险。同时，为了关联books和books_category表，使用了SELECT INTO语句。