$aColumns = array( 'imie', 'nazwisko', 'miejsce_ur', 'praca' );

$sOutput .= '"select": [ ';

//select lists
for ( $i=0; $i<count($aColumns); $i++ )
{
    $sQuery = "
    SELECT DISTINCT ".$aColumns[$i]."
    FROM   $sTable
    ";

    $rSelectList = mysql_query( $sQuery, $gaSql['link'] ) or die(mysql_error());

    $row = array();
    while ( $aRow = mysql_fetch_array( $rSelectList ) )
    {
        $row[] = $aRow[ $aColumns[$i] ];
    }
    $output['select'][] = $row;
}

$sOutput = substr_replace( $sOutput, "", -1 );
$sOutput .= '] }';

echo $sOutput;