simple pdo wrapper, only tested on mysql

<?php

/* add your database login details to db::connect() */

/* sample usage */

/*
$sql = "drop table if exists db_test";
db::query($sql);
echo "dropping table db_test\n";


$sql = "create table db_test(id int auto_increment primary key, name varchar(100), number int)";
db::query($sql);
echo "<hr>creating table db_test\n";


$sql = "insert into db_test(name, number) values (:name, :number)";
$arr = array(":name" => "Hello", ":number" => 44);
$id = db::query($sql, $arr);
echo "<hr>sample insert, id: $id\n";


$sql = "insert into db_test(name, number) values (:name, :number)";
$arr = array(":name" => "World", ":number" => 55);
$id = db::query($sql, $arr);
echo "<hr>second insert, id: $id\n";


$sql = "update db_test set number = :number";
$arr = array(":number" => 77);
$rows_affected = db::query($sql, $arr);
echo "<hr>sample update, $rows_affected rows affected\n";


$sql = "select * from db_test where name like :name";
$arr = array(":name" => "%");
$result = db::query($sql, $arr);
echo "<hr>sample select returns an array of rows,<br>\n";
if(count($result) == 0)
    echo "no records found<br>.\n";
foreach($result as $row){
    echo htmlentities($row['id'] . ' ' . $row['name'] . ' ' . $row['number']) . "<br>\n";
}


$sql = "select * from db_test where id = :id";
$arr = array(":id" => 1);
$row = db::query_row($sql, $arr);
echo "<hr>sample select using query_row() to return a single row array,<br>\n";
if(!$row)
    echo "row not found\n";
else
    echo "row found: " . htmlentities($row['id'] . ' ' . $row['name'] . ' ' . $row['number']) . "\n";


$sql = "select name from db_test where id = :id";
$arr = array(":id" => 1);
$val = db::query_val($sql, $arr);
echo "<hr>sample select using query_val() to return a single value,<br>\n";
if(!$val)
    echo "value not found\n";
else
    echo "value found: " . htmlentities($val) . "\n";


db::connect();
db::$dbh->beginTransaction(); // speed up multi inserts with a transaction
for($i = 0; $i < 1000; $i++){
    $sql = "insert into db_test(name, number) values (:name, :number)";
    $arr = array(":name" => "Name $i", ":number" => $i);
    db::query($sql, $arr);
}
db::$dbh->commit(); // commit transaction
echo "<hr>inserted $i records in a transaction\n";


$sql = "delete from db_test where number = :number or 1=1";
$arr = array(":number" => 66);
$rows_affected = db::query($sql, $arr);
echo "<hr>sample delete, $rows_affected rows affected\n";

*/

class db{

    // purpose: simple pdo wrapper, only tested on mysql

    // configure settings in connect()
    private static $db_connection_string = null;
    private static $db_user = null;
    private static $db_pass = null;
    private static $display_error_detail = null;

    public static $dbh = null;

    public static function connect(){

        if(self::$dbh)
            return;

       // *** edit this block according to how you detect your enviroment ***
        if(getenv('ENV') == 'development'){
            self::$db_connection_string = 'mysql:host=localhost;dbname=test;';
            self::$db_user = 'root';
            self::$db_pass = '';
            self::$display_error_detail = true; // show full error in development
        }
        else{
            self::$db_connection_string = 'mysql:host=localhost;dbname=test;';
            self::$db_user = 'root';
            self::$db_pass = '';
            self::$display_error_detail = false; // hide errors in production, only "query error" is displayed
        }

        try{
            self::$dbh = new PDO(self::$db_connection_string, self::$db_user, self::$db_pass);
        }
        catch(PDOException $e){
            die('pdo connection error: ' . $e->getMessage());
        }
    }


    public static function query($sql, $sql_param = array()){

        // purpose: run a query
        // returns:
        //   array of rows for selects
        //   false on errors
        //   id for insert statements
        //   # rows affected for updates and deletes

        self::connect();
        $sth = self::$dbh->prepare($sql);

        // handle errors
        if(!$sth->execute($sql_param)){
            $arr = $sth->errorInfo();
            $error = $arr[2];

            if(self::$display_error_detail)
                echo "<pre style='color: red;'>" . htmlentities("Error: $error\n\n$sql\n\n") . "Parameters:\n" . print_r($sql_param, true) . "</pre>";
            else
                echo "<pre style='color: red;'>query error</pre>";

            return false;
        }

        // return insert id for insert and rows affected for update, delete, and replace
        if(preg_match('/^\s*(insert|replace)/i', $sql))
            return self::$dbh->lastInsertId();
        elseif(preg_match('/^\s*(update|delete)/i', $sql))
            return $sth->rowCount();

        if($sth->columnCount() == 0)
            return array();

        return $sth->fetchAll(PDO::FETCH_ASSOC);

    }


    public static function query_row($sql, $sql_param = array()){

        // purpose: wrapper for query()
        // returns:
        //   a single row array
        //   returns null when no results are found
        //   returns false on errors

        $result = self::query($sql, $sql_param);

        if($result === false)
            return false;
        elseif(is_array($result) && count($result) > 0)
            return current($result);
        else
            return null;
    }


    public static function query_val($sql, $sql_param = array()){

        // purpose: wrapper for query()
        // returns:
        //   a single value
        //   returns null when no results are found
        //   returns false on errors

        $result = self::query($sql, $sql_param);

        if($result === false)
            return false;
        elseif(is_array($result) && count($result) > 0)
            return current(current($result));
        else
            return null;
    }

}