Is there a way to fetch associative array grouped by the values of a specified column with PDO?

Question

For example, let\'s use some simple data set

+---------+------+------+------------+
| name    | age  | sex  | position   |
+---------+------+------+---------         


        

Answer 1

This answer is out of date, please see this other answer instead.

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It looks like there's no way to do this as part of fetchAll.

Your best bet is going to be creating a class that extends PDO, adding a utility method to it.

public function queryKeyedAssoc($query, $params, $key) {
    $sth = $this->prepare($query);
    $sth->execute($params);
    $res = array();
    while($row = $sth->fetch(PDO::FETCH_ASSOC))
        $res[ $row[$key] ] = $row;
    return $res;
}

Answer 2

We can make Charles' solution a little nicer by extending the statement class instead:

class MyPdo extends PDO {
    function __construct($host, $database_name, $username, $password, $options=array()) {
        $options = self::merge(array(
            PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
            PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
            PDO::ATTR_STATEMENT_CLASS => array('PdoPlusStatement', array()),
            PDO::ATTR_EMULATE_PREPARES => true,
            PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8',
        ), $options);
        $dsn = "mysql:host=$host;dbname=$database_name;charset=utf8";
        parent::__construct($dsn, $username, $password, $options);
    }
}

class PdoPlusStatement extends PDOStatement {
    protected function __construct() {}

    /**
     * @param array|mixed $input_parameters An array of values with as many elements as there are bound parameters in the SQL statement being executed, or one or more non-array arguments to be matched with sequential parameter markers.
     * @throws PDOException
     * @return PdoPlusStatement
     */
    public function execute($input_parameters=null) {
        $args = func_get_args();
        $argc = func_num_args();
        if($argc===0) {
            parent::execute();
        } else {
            if($argc===1 && is_array($args[0])) {
                $args = $args[0];
            }
            parent::execute($args);
        }
        return $this;
    }

    /**
     * Returns an array containing all of the remaining rows in the result set
     * @return array An associative array using the first column as the key, and the remainder as associative values
     */
    public function fetchKeyAssoc() {
        return array_map('reset', $this->fetchAll(PDO::FETCH_GROUP|PDO::FETCH_ASSOC));
    }
}

Usage:

$users = $pcs->query("SELECT name, user_id, discipline_id FROM wx_user")->fetchKeyAssoc();

Answer 3

Not sure why no one has posted the following solution, but it works perfectly for me:

PDO::FETCH_UNIQUE | PDO::FETCH_ASSOC

So, changing your statement to:

$pdo->query('SELECT * FROM employee')->fetchAll(PDO::FETCH_UNIQUE|PDO::FETCH_ASSOC);

should be exactly what you want.

Answer 4

It's quite old topic, but I found very easy solution:

->fetchAll(\PDO::FETCH_GROUP|\PDO::FETCH_UNIQUE)

First col will be set as key, rest will be set as value.

No need to walk over the array or use array_map.

Answer 5

The accepted answer is essentially a cargo cult code, that does its job only by accident, but makes no sense by itself.

PDO::FETCH_GROUP and PDO::FETCH_UNIQUE are mutual exclusive fetch modes, that cannot be used together. Only one of them would work. When you combine them, the latter takes over and \PDO::FETCH_GROUP|\PDO::FETCH_UNIQUE is actually just PDO::FETCH_UNIQUE.

Beside that, the question is ambiguous by itself, the OP wants his array to be indexed by the unique field, whereas he called it grouping which raised a controversy in the answers as well.

So to make it straight:

• to index an array with unique values (when you want the resulting array to be indexed by the employee's name, given they are unique), the fetch mode must be PDO::FETCH_UNIQUE:

  $pdo->query('SELECT name, e.* FROM employee e')->fetchAll(PDO::FETCH_UNIQUE);
  

• to group the results (when you want to group employees by department, for example), the fetch mode must be PDO::FETCH_GROUP:

  $pdo->query('SELECT dept_id, e.* FROM employee e')->fetchAll(PDO::FETCH_GROUP);
  

in both cases the field to be used as the first level array index, must be listed first in the SELECT field list.

A note on the PDO::FETCH_ASSOC. Given that fetch mode for the preferred result format could be set once for all in the constructor, it makes no sense to list it explicitly as well.

Answer 6

to reduce a unnecessary nesting array level:

$res = $pdo->query('SELECT * FROM employee')->fetchAll(PDO::FETCH_GROUP|PDO::FETCH_ASSOC);
$res = array_map('reset', $res);