Why am I getting "Trying to access array offset on value of type bool" when using a while loop?

Question

I have a PDO object with the following code:

$query = "SELECT DISTINCT SUBSTR( Date(Date), 1, 4) AS YEAR from Events ORDER BY YEAR DESC;";
$sth = $dbh->query( $query );
while( $row = $sth->fetch( PDO::FETCH_ASSOC )['YEAR'] ) {
  print $row
}

The code executes, but I get

Trying to access array offset on value of type bool

What is the explanation, and is there a solution?

Answer 1

The way that a while loop works is that it will keep on iterating as long as the condition evaluates to a boolean true.

PDOStatement::fetch() will return an array containing the data of the current row and move an internal pointer to the next row in the result. If there are no more rows, it returns false .

This means that once you reach the end of the PDO result, fetch() returns false and you can't access array offset on false . This is why you get an error.

There are a couple of ways to solve this problem.

1. Don't use while loop. There's no reason to use it in your example.

    foreach ($sth as $row) { echo $row['YEAR']; }

2. If all you want is a single column then there's no reason to fetch an array.

    while( $year = $sth->fetchColumn() ) { echo $year; }

3. Set the fetch mode when you execute the query or using setFetchMode() .

    $sth = $dbh->query( $query, PDO::FETCH_COLUMN, 0 ); foreach ($sth as $year) { echo $year; }

Answer 2

This seems to work too:

$sth = $dbh->query( $query );
while( $row = $sth->fetch( PDO::FETCH_ASSOC ))
  print $row['YEAR']

I agree that foreach is more appropriate