(PHP 5 >= 5.1.0, PECL pdo >= 0.1.0)
PDOStatement::fetchAll — Returns an array containing all of the result set rows
$fetch_style
   [, mixed $fetch_argument
   [, array $ctor_args = array()
  ]]] )
fetch_style
       Controls the contents of the returned array as documented in
       PDOStatement::fetch().
       Defaults to value of PDO::ATTR_DEFAULT_FETCH_MODE
       (which defaults to PDO::FETCH_BOTH)
      
       To return an array consisting of all values of a single column from
       the result set, specify PDO::FETCH_COLUMN. You
       can specify which column you want with the
       fetch_argument parameter.
      
       To fetch only the unique values of a single column from the result set,
       bitwise-OR PDO::FETCH_COLUMN with
       PDO::FETCH_UNIQUE.
      
       To return an associative array grouped by the values of a specified
       column, bitwise-OR PDO::FETCH_COLUMN with
       PDO::FETCH_GROUP.
      
fetch_argument
       This argument has a different meaning depending on the value of 
       the fetch_style parameter:
       
          PDO::FETCH_COLUMN: Returns the indicated 0-indexed 
           column.
         
          PDO::FETCH_CLASS: Returns instances of the specified
          class, mapping the columns of each row to named properties in the class.
         
          PDO::FETCH_FUNC: Returns the results of calling the
          specified function, using each row's columns as parameters in the call.
         
ctor_args
       Arguments of custom class constructor when the fetch_style 
       parameter is PDO::FETCH_CLASS.
      
   PDOStatement::fetchAll() returns an array containing
   all of the remaining rows in the result set. The array represents each
   row as either an array of column values or an object with properties
   corresponding to each column name. An empty array is returned if there
   are zero results to fetch, or FALSE on failure.
  
Using this method to fetch large result sets will result in a heavy demand on system and possibly network resources. Rather than retrieving all of the data and manipulating it in PHP, consider using the database server to manipulate the result sets. For example, use the WHERE and ORDER BY clauses in SQL to restrict results before retrieving and processing them with PHP.
Example #1 Fetch all remaining rows in a result set
<?php
$sth = $dbh->prepare("SELECT name, colour FROM fruit");
$sth->execute();
/* Fetch all of the remaining rows in the result set */
print("Fetch all of the remaining rows in the result set:\n");
$result = $sth->fetchAll();
print_r($result);
?>
The above example will output something similar to:
Fetch all of the remaining rows in the result set:
Array
(
    [0] => Array
        (
            [name] => pear
            [0] => pear
            [colour] => green
            [1] => green
        )
    [1] => Array
        (
            [name] => watermelon
            [0] => watermelon
            [colour] => pink
            [1] => pink
        )
)
Example #2 Fetching all values of a single column from a result set
The following example demonstrates how to return all of the values of a single column from a result set, even though the SQL statement itself may return multiple columns per row.
<?php
$sth = $dbh->prepare("SELECT name, colour FROM fruit");
$sth->execute();
/* Fetch all of the values of the first column */
$result = $sth->fetchAll(PDO::FETCH_COLUMN, 0);
var_dump($result);
?>
The above example will output something similar to:
Array(3)
(
    [0] =>
    string(5) => apple
    [1] =>
    string(4) => pear
    [2] =>
    string(10) => watermelon
)
Example #3 Grouping all values by a single column
The following example demonstrates how to return an associative array grouped by the values of the specified column in the result set. The array contains three keys: values apple and pear are returned as arrays that contain two different colours, while watermelon is returned as an array that contains only one colour.
<?php
$insert = $dbh->prepare("INSERT INTO fruit(name, colour) VALUES (?, ?)");
$insert->execute(array('apple', 'green'));
$insert->execute(array('pear', 'yellow'));
$sth = $dbh->prepare("SELECT name, colour FROM fruit");
$sth->execute();
/* Group values by the first column */
var_dump($sth->fetchAll(PDO::FETCH_COLUMN|PDO::FETCH_GROUP));
?>
The above example will output something similar to:
array(3) {
  ["apple"]=>
  array(2) {
    [0]=>
    string(5) "green"
    [1]=>
    string(3) "red"
  }
  ["pear"]=>
  array(2) {
    [0]=>
    string(5) "green"
    [1]=>
    string(6) "yellow"
  }
  ["watermelon"]=>
  array(1) {
    [0]=>
    string(5) "green"
  }
}
Example #4 Instantiating a class for each result
     The following example demonstrates the behaviour of the
     PDO::FETCH_CLASS fetch style.
    
<?php
class fruit {
    public $name;
    public $colour;
}
$sth = $dbh->prepare("SELECT name, colour FROM fruit");
$sth->execute();
$result = $sth->fetchAll(PDO::FETCH_CLASS, "fruit");
var_dump($result);
?>
The above example will output something similar to:
array(3) {
  [0]=>
  object(fruit)#1 (2) {
    ["name"]=>
    string(5) "apple"
    ["colour"]=>
    string(5) "green"
  }
  [1]=>
  object(fruit)#2 (2) {
    ["name"]=>
    string(4) "pear"
    ["colour"]=>
    string(6) "yellow"
  }
  [2]=>
  object(fruit)#3 (2) {
    ["name"]=>
    string(10) "watermelon"
    ["colour"]=>
    string(4) "pink"
  }
}
Example #5 Calling a function for each result
     The following example demonstrates the behaviour of the
     PDO::FETCH_FUNC fetch style.
    
<?php
function fruit($name, $colour) {
    return "{$name}: {$colour}";
}
$sth = $dbh->prepare("SELECT name, colour FROM fruit");
$sth->execute();
$result = $sth->fetchAll(PDO::FETCH_FUNC, "fruit");
var_dump($result);
?>
The above example will output something similar to:
array(3) {
  [0]=>
  string(12) "apple: green"
  [1]=>
  string(12) "pear: yellow"
  [2]=>
  string(16) "watermelon: pink"
}