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(PHP 5 >= 5.1.0, PECL pdo >= 0.2.0)
PDO::query — Executes an SQL statement, returning a result set as a PDOStatement object
$statement 
   )$statement 
   ,  int $PDO::FETCH_COLUMN 
   ,  int $colno 
   )$statement 
   ,  int $PDO::FETCH_CLASS 
   ,  string $classname 
   ,  array $ctorargs 
   )$statement 
   ,  int $PDO::FETCH_INTO 
   ,  object $object 
   )PDO::query() executes an SQL statement in a single function call, returning the result set (if any) returned by the statement as a PDOStatement object.
For a query that you need to issue multiple times, you will realize better performance if you prepare a PDOStatement object using PDO::prepare() and issue the statement with multiple calls to PDOStatement::execute() .
If you do not fetch all of the data in a result set before issuing your next call to PDO::query() , your call may fail. Call PDOStatement::closeCursor() to release the database resources associated with the PDOStatement object before issuing your next call to PDO::query() .
Note:
Although this function is only documented as having a single parameter, you may pass additional arguments to this function. They will be treated as though you called PDOStatement::setFetchMode() on the resultant statement object.
statement The SQL statement to prepare and execute.
Data inside the query should be properly escaped.
  PDO::query()  returns a PDOStatement object, or  FALSE 
    on failure.
  
Example #1 Demonstrate PDO::query
A nice feature of PDO::query() is that it enables you to iterate over the rowset returned by a successfully executed SELECT statement.
  <?php
 function  getFruit ( $conn ) {
     $sql  =  'SELECT name, color, calories FROM fruit ORDER BY name' ;
    foreach ( $conn -> query ( $sql ) as  $row ) {
        print  $row [ 'name' ] .  "\t" ;
        print  $row [ 'color' ] .  "\t" ;
        print  $row [ 'calories' ] .  "\n" ;
    }
}
 ?>   以上例程会输出:
apple red 150 banana yellow 250 kiwi brown 75 lemon yellow 25 orange orange 300 pear green 150 watermelon pink 90
[#1] tgrl5000 [2015-05-21 15:42:16]
Connecting
==============================
<?php
try{
 $db = new PDO("dbtype:host=yourhost;dbname=yourdbname;charset=utf8","username","password");
}catch(PDOException  $e ){
echo "Error: ".$e;
}
?>
Excute query with secure data
==============================
<?php
try{
 $db = new PDO("dbtype:host=yourhost;dbname=yourdbname;charset=utf8","username","password");
$mysecuredata=14;
$db->query("Select * from table where id=".$mysecuredata);
}catch(PDOException  $e ){
echo "Error: ".$e;
}
?>
Excute query with insecure data
==============================
<?php
try{
 $db = new PDO("dbtype:host=yourhost;dbname=yourdbname;charset=utf8","username","password");
$myinsecuredata=$_GET["id"];
$query=$db->prepare("Select * from table where id=?");
$query->excute(array($myinsecuredata));
}catch(PDOException  $e ){
echo "Error: ".$e;
}
?>
Getting Data in database
==============================
<?php
try{
 $db = new PDO("dbtype:host=yourhost;dbname=yourdbname;charset=utf8","username","password");
$myinsecuredata=$_GET["table"];
$query=$db->prepare("Select * from ?");
$query->excute(array($myinsecuredata));
 while($row=$query->fetch(PDO::FETCH_OBJ)) {
        echo $row->yourcolumnname;
    }
}catch(PDOException  $e ){
echo "Error: ".$e;
}
?>
Reference
==============================
http://gencbilgin.net/pdo-kullanimi-php-de-veritabani-islemleri.html
[#2] stefano[dot]bertoli [at] gmail[dot]com [2014-09-08 14:14:51]
Trying to pass like second argument PDO::FETCH_ASSOC it still work.
So passing FETCH TYPE like argument seems work.
This save you from something like:
<?php
$result = $stmt->setFetchMode(PDO::FETCH_NUM);
?>
Example:
<?php
$res = $db->query('SELECT * FROM `mytable` WHERE true', PDO::FETCH_ASSOC);
?>
[#3] paolo at dellunto dot net [2013-10-13 23:21:08]
If you are using PDO to create an SQLite dbfile that will be used by an Android application, you can set common values via the $dbh->query("PRAGMA ...") statement;
a tipical example would be the user_version of the database or the page_size 
<?php
...
$dbh = new PDO($PDO_DSN, null, null, null);
$dbh->query("PRAGMA page_size = 4096"); //Android match page size
$dbh->query("PRAGMA user_version = 2"); //This match super(context, DB_NAME, null, DB_VERSION) of the DatabaseOpenHelper
....
?>
[#4] marcos at marcosregis dot com [2008-09-24 09:14:18]
After a lot of hours working with DataLink on Oracle->MySQL and PDO we (me and Adriano Rodrigues, that solve it) discover that PDO (and oci too) need the attribute AUTOCOMMIT set to FALSE to work correctly with.
There's  3 ways to set autocommit to false: On constructor, setting the atribute after construct and before query data or initiating a Transaction (that turns off autocommit mode)
The examples:
<?php
// First way - On PDO Constructor
$options = array(PDO::ATTR_AUTOCOMMIT=>FALSE);
$pdo = new PDO($dsn,$user,$pass,$options);
// now we are ready to query DataLinks
?>
<?php 
// Second Way - Before create statements
$pdo = new PDO($dsn,$user,$pass);
$pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,FALSE);
// or
$pdo->beginTransaction();
// now we are ready to query DataLinks
?>
To use DataLinks on oci just use OCI_DEFAULT on oci_execute() function;
[#5] andrea at bhweb dot it [2008-07-16 03:57:23]
If someone is suffering of the "MySQL server has gone away" problem after executing multiple queries, this is a solution that solved it for me. It's similar to the one needed for the exact same problem in mysqli.
<?php
$stmt=$db->prepare($query);
$stmt->execute();
do { $stmt->fetch(); $stmt->closeCursor(); ++$line; } while($stmt-
>nextRowset());
?>
I found this only works using prepare and execute this way, not if you 
directly execute the query with query().
[#6] NUNTIUS [2008-01-22 09:01:11]
I found this method extremely useful for getting the iteration count. Note the usage of "for" instead of "while" or "foreach". Just place the "$row = $query->fetch()" as the second condition of your for loop (which is do until). This is the best of both worlds IMHO. Criticism welcome.
try {
    $hostname = "servername";
    $dbname = "dbname";
    $username = "username";
    $pw = "password";
	$pdo = new PDO ("mssql:host=$hostname;dbname=$dbname","$username","$pw");
  } catch (PDOException $e) {
    echo "Failed to get DB handle: " . $e->getMessage() . "\n";
    exit;
  }
	  $query = $pdo->prepare("select name FROM tbl_name");
	  $query->execute();
	  
	  for($i=0; $row = $query->fetch(); $i++){
		echo $i." - ".$row['name']."<br/>";
	  }
	  unset($pdo); 
	  unset($query);
[#7] fredrik at NOSPAM dot rambris dot com [2007-05-05 09:04:15]
The handling of errors by this function is controlled by the attribute PDO::ATTR_ERRMODE.
Use the following to make it throw an exception:
<?php
$dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
?>
[#8] nicobn at gmail dot com [2007-04-26 15:29:48]
Please note that when Query() fails, it does not return a PDOStatement object . It simply returns false.
[#9] jonmsawyer at gmail dot com [2007-01-23 12:03:41]
@ dozoyousan at gmail dot com
> 03-May-2006 05:26
> > When query() fails, the boolean false is returned.
>
> I think that is "Silent Mode".
> If that set attribute ErrorMode "Exception Mode"
> then that throw PDOException.
> $pdoObj = new PDO( $dsn, $user, $pass );
> $pdoObj->setAttribute("PDO::ATTR_ERRMODE",
> PDO::ERRMODE_EXCEPTION);
What you say is correct, however, your PHP code is incorrect:
<?php
    // This is fine
    $pdoObj = new PDO( $dsn, $user, $pass );
    
    // This line is wrong
    $pdoObj->setAttribute("PDO::ATTR_ERRMODE", PDO::ERRMODE_EXCEPTION);
    
    // It should be:
    $pdoObj->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    
    // Parameter 1 should not be in quotes. PHP interprets
    // that as a string. Instead, internally, its represented
    // as type LONG INT. Try it :)
?>
Hope this helps. Cheers.
[#10] dozoyousan at gmail dot com [2006-05-02 22:26:29]
> When query() fails, the boolean false is returned. 
I think that is "Silent Mode".
If that set attribute ErrorMode "Exception Mode"
then that throw PDOException.
 $pdoObj = new PDO( $dsn, $user, $pass );
 $pdoObj->setAttribute("PDO::ATTR_ERRMODE", PDO::ERRMODE_EXCEPTION);