Question

如何检查列值是否为空？示例代码：

$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

当您连接到数据库时，您可以设置一些属性来控制PDO在数据库查询返回时处理Null和空字符串的方式

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

其中$ option是以下之一：

PDO :: NULL_NATURAL：无转换。
PDO :: NULL_EMPTY_STRING：空字符串转换为NULL。
PDO :: NULL_TO_STRING：NULL转换为空字符串。

Answer 2

这不是你想做的吗？

foreach($row as $r){

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

  //do something

}

其实您可能想尝试：

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

因为php可能已经将null值转换为空字符串，然后它实际上不是null，所以它是“”

希望这有帮助！

Answer 3

感谢您的所有答案。经过一些实验，这段代码解决了我的问题

$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!!!
{
...
}

PHP PDO获取null

3 个答案: