pdo get field names

[John Smith]

I'm using PDO for the first time. I want to get the field/column names
from a SELECT query. I can get the names from the associative array
returned by fetch(). But how do I get the field names if the SELECT
query returns no rows? I could do this before with the
xxxx_fetch_field() functions.

Here's a condensed version of my code:

// query the database
$DbToQuery = new PDO("sqlite::memory:");
$DbToQuery->query("CREATE TABLE MyTable (MyField TEXT)");
$sql = "SELECT * FROM MyTable";
$result = $DbToQuery->query($sql);
// Get the number of columns
$Cols = $result->columnCount();
// Loop through the results
$countrows = 1;
while($row = $result->fetch(PDO::FETCH_ASSOC)) {
if($countrows == 1) {
// Print column names
print join(",", array_keys($row));
}
$countrows++;
// handle the row data
// ...
}