插入失败的SQLITE &PHP PDO -一般错误:25绑定或列索引超出范围

我试图在Slim框架内使用PHP PDO函数插入一些数据到我的数据库中，但当我使用curl发布时，我得到以下错误;

SQLSTATE[HY000]: error: bind or column index out of range

我使用的curl命令是;

curl -i -X POST -H 'Content-Type: application/json' -d '{"category_name":"cat3",     "item_name":"test"}' http://localhost/api/add

这个PHP函数是;

function addContent() {
    $request = 'Slim'Slim::getInstance()->request();
    $content = json_decode($request->getBody());
    $sql = "insert into category (category_name) values (:category_name);
    insert into item (category_id,item_name) values 
    ((select category_id from category where category_name = :category_name2),     :item_name);";
    try {
        $db = getConnection();
        $stmt = $db->prepare($sql);
        $stmt->bindParam("category_name", $content->category_name);
        $stmt->bindParam("category_name2", $content->category_name);
        $stmt->bindParam("item_name", $content->item_name);
        $stmt->execute();
        $db = null;
        echo json_encode($content);
    } catch(PDOException $e) {
        echo '{"error":{"text":'. $e->getMessage() .'}}';
    }
}

sql基本上是在类别表中添加一个新类别，然后在引用新创建的类别的项表中添加一个新项。如果我在sqlite中运行查询，那么它似乎添加所需的行很好，查询是;

insert into category(category_name) values ('cat2');
insert into item (category_id,item_name) values
((select category_id from category where category_name = 'cat2'),'item3');

我为已经存在的类别写了一些类似的东西，似乎工作得很好;

同类工作函数

function addContent() {
    $request = 'Slim'Slim::getInstance()->request();
    $content = json_decode($request->getBody());
    $sql = "insert into item (category_id,item_name) values
((select category_id from category where category_name = :category_name), :item_name);";
    try {
        $db = getConnection();
        $stmt = $db->prepare($sql);
        $stmt->bindParam("category_name", $content->category_name);
        $stmt->bindParam("item_name", $content->item_name);
        $stmt->execute();
        $db = null;
        echo json_encode($content);
    } catch(PDOException $e) {
        echo '{"error":{"text":'. $e->getMessage() .'}}';
    }
}

通过阅读，我认为我需要分别设置两个:category_name引用，这就是为什么我有:category_name &: category_name2。否则，据我所知，这应该像预期的那样工作。如有任何建议，不胜感激。

工作功能由IMSoP提供;珀斯的答案

现在按要求工作，虽然可能不是最漂亮的解决方案，但完成了工作。谢谢你们的建议。

function addContent() {
    $request = 'Slim'Slim::getInstance()->request();
    $content = json_decode($request->getBody());
    $sql_category = "insert into category (category_name) values (:category_name);";
    $sql_item = "insert into item (category_id,item_name) values 
((select category_id from category where category_name = :category_name),     :item_name);";
    try {
        $db = getConnection();
        $stmt_category = $db->prepare($sql_category);
        $stmt_category->bindParam("category_name", $content->category_name);
        $stmt_category->execute();
        $stmt_item = $db->prepare($sql_item);
        $stmt_item->bindParam("category_name", $content->category_name);
        $stmt_item->bindParam("item_name", $content->item_name);
        $stmt_item->execute();
        $db = null;
        echo json_encode($content);
    } catch(PDOException $e) {
        echo '{"error":{"text":'. $e->getMessage() .'}}';
    }
}