PHP PDO獲取null

Question

如何檢查列值是否為空？ 示例代碼：

$db = DBCxn::getCxn();

$sql = "SELECT exercise_id, author_id, submission, result, submission_time, total_rating_votes, total_rating_values
FROM submissions 
LEFT OUTER JOIN submission_ratings ON submissions.exercise_id=submission_ratings.exercise_id
WHERE id=:id";

$st = $db->prepare($sql);

$st->bindParam(":id", $this->id, PDO::PARAM_INT);

$st->execute();
$row = $st->fetch();

$this->total_rating_votes = $row['total_rating_votes'];

if($this->total_rating_votes == null) // this doesn't seem to work even though there is no record in submission_ratings????
{
...
}

Answer 1

連接到數據庫時，可以設置一些屬性來控制PDO在數據庫查詢返回時如何處理Null和Empty Strings

PDO :: setAttribute（PDO :: ATTR_ORACLE_NULLS，$ option）

其中$ option是以下之一：

• PDO :: NULL_NATURAL：無轉換。
• PDO :: NULL_EMPTY_STRING：空字符串轉換為NULL。
• PDO :: NULL_TO_STRING：NULL轉換為空字符串。

Answer 2

不是你想做的事嗎？

foreach($row as $r){

if($r->total_rating_votes == null){

  //do something

}

其實你可能想嘗試：

if($r->total_rating_votes == ""){/*do something*/}

因為php可能已經將null值轉換為空字符串，然后它實際上不是null，所以它是“”

希望這可以幫助！

Answer 3

謝謝你的所有答案。 經過一些實驗，這段代碼解決了我的問題

$this->total_rating_votes = $row['total_rating_votes'];

if(!isset($this->total_rating_votes)) // this is now true if this record had a NULL value in the DB!!!
{
...
}