CODEWITHSUNDEEP
phpmysqlpdoprepared-statement
cdwhatcott
cdwhatcott

Reputation: 472

Selecting rows where a field is null using PHP PDO prepared statements and MySQL

I've been converting an app to use PDO prepared statements rather than mysqli and I'm running into a strange problem. I have some records in the database where it's expected that a field will be null. Not 'null' (string), or '' (empty string), but NULL. I build my queries dynamically, so in the past when I came across a null variable in an object, I'd build the query like this:

WHERE fieldName is null;

And would get the expected results when the field was null.

Now with PDO, my queries aren't returning any results and I'm not getting any errors. It just simply isn't returning the records I would expect. When I echo the built queries and run them directly in MySQL I get the expected results, but within the application there are no results returned.

Some of the things I've tried include building queries that look like this:

WHERE fieldName is null;

or

WHERE fieldName <=> null;

I have also tried the standard prepared statement of: 

WHERE fieldName = :fieldName

and then binding with these kinds of statements:

$stmt->bindParam(":$field", $value);
$stmt->bindParam(":$field", $value, PDO::PARAM_NULL);
$stmt->bindParam(":$field", null, PDO::PARAM_NULL);
$stmt->bindValue(":$field", null, PDO::PARAM_NULL);
$stmt->bindValue(":$field", null, PDO::PARAM_INT);

Any help with this would be greatly appreciated. My PHP version is 5.3.10 and MySQL is 5.5.22. As a side question, I still am not clear on the difference between bindParam and bindValue, so if it makes sense to include in your answer I would really appreciate some clarification on the subject...

Upvotes: 16

Views: 12322

Answers (3)

cdwhatcott
cdwhatcott

Reputation: 472

Since this question has been written, mysql introduced a spaceship operator that allows us to use a regular query to match a null value

WHERE fieldName <=> :fieldName;

will match both a null or any not null value.

So just write your query right away and execute it as usual

$stmt = $db->prepare('SELECT field FROM table WHERE fieldName <=> :fieldName;');
$stmt->execute(['fieldName' => null]);
$result = $stmt->fetchAll(); // whatever fetch method is suitable

And with dynamically built queries it's all the same.

Upvotes: 13

Abul Fayes
Abul Fayes

Reputation: 147

In MySql you can use the query 

select * from atable where isnull(column_name);

to check for null values.

Upvotes: -2

Green Black
Green Black

Reputation: 5084

Different question, but all awnsers are in here: How do I insert NULL values using PDO?

To sum it up:

$stmt->bindValue(':param', null, PDO::PARAM_INT);

Should work.You can also use:

$stmt->execute( array(":param" => NULL));

For bindparam you must give the value in a variable (not a constant), bindvalue you can use constants etc.

Upvotes: -2

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