PDO的连接通过创建pdo基础类时实现，无须其他驱动，你只需要使用PDO类名。该构造器参数需指明数据库来源，根据连接需要提供数据库的用户名和密码参数。
一个连接mysql的例子：
$dbh = new PDO('mysql:host=localhost;dbname=test', $user, $pass);
如果在连接过程中产生错误，PDO异常对象将抛出。如果你想处理这些错误情况就可以捕捉这些异常。
处理连接错误的例子：
try {
$dbh = new PDO('mysql:host=localhost;dbname=test', $user, $pass);
foreach($dbh->query('Select * from FOO') as $row) {
print_r($row);
}
$dbh = null;
} catch (PDOException $e) {
print "Error!: \" . $e->getMessage() . \"
\";
die();
}
?> 持续连接：
$dbh = new PDO('mysql:host=localhost;dbname=test', $user, $pass, array(
PDO::ATTR_PERSISTENT => true
));
?>
考虑了下，最终还是决定用pdo来操作sqlite3，因为技术上新的东西应该比旧的要好。pdo作为php的下一代标准数据接口会在php6中广泛应用，虽然php6正式发行版还遥遥无期。pdo的优势是很明显的，对于数据库的操作统一且易于数据库变动升级，而不需大面积修改源码。以前操作不同数据库需要用完全不同的函数，现在只需要在连接时用参数区分不同数据库，操作完全统一。至于sqlite2和3的区别并不了解，不过从sqlite3完全不向下兼容2，说明改动还是挺大的，应该有不少优势，只是我还不知道！
预定义常量：
The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.
PDO::PARAM_BOOL (integer) 表示一个布尔数据类型。 PDO::PARAM_NULL (integer)表示一个SQL NULL 数据类型。PDO::PARAM_INT (integer)表示一个SQL INTEGER 数据类型。PDO::PARAM_STR (integer)Represents the SQL CHAR, VARCHAR, or other string data type.PDO::PARAM_LOB (integer)Represents the SQL large object data type.PDO::PARAM_STMT (integer)表示一个记录集类型。当前无任何驱动支持。PDO::PARAM_INPUT_OUTPUT (integer)Specifies that the parameter is an INOUT parameter for a stored procedure. You must bitwise-OR this value with an explicit PDO::PARAM_* data type.PDO::FETCH_LAZY (integer)Specifies that the fetch method shall return each row as an object with variable names that correspond to the column names returned in the result set. PDO::FETCH_LAZY creates the object variable names as they are accessed.PDO::FETCH_ASSOC (integer)Specifies that the fetch method shall return each row as an array indexed by column name as returned in the corresponding result set. If the result set contains multiple columns with the same name, PDO::FETCH_ASSOC returns only a single value per column name.PDO::FETCH_NAMED (integer)Specifies that the fetch method shall return each row as an array indexed by column name as returned in the corresponding result set. If the result set contains multiple columns with the same name, PDO::FETCH_NAMED returns an array of values per column name.PDO::FETCH_NUM (integer)Specifies that the fetch method shall return each row as an array indexed by column number as returned in the corresponding result set, starting at column 0.PDO::FETCH_BOTH (integer)Specifies that the fetch method shall return each row as an array indexed by both column name and number as returned in the corresponding result set, starting at column 0.PDO::FETCH_OBJ (integer)Specifies that the fetch method shall return each row as an object with property names that correspond to the column names returned in the result set.PDO::FETCH_BOUND (integer)Specifies that the fetch method shall return TRUE and assign the values of the columns in the result set to the PHP variables to which they were bound with the PDOStatement::bindParam() or PDOStatement::bindColumn() methods.PDO::FETCH_COLUMN (integer)Specifies that the fetch method shall return only a single requested column from the next row in the result set.PDO::FETCH_CLASS (integer)Specifies that the fetch method shall return a new instance of the requested class, mapping the columns to named properties in the class.PDO::FETCH_INTO (integer)Specifies that the fetch method shall update an existing instance of the requested class, mapping the columns to named properties in the class.PDO::FETCH_FUNC (integer)PDO::FETCH_GROUP (integer)PDO::FETCH_UNIQUE (integer)PDO::FETCH_KEY_PAIR (integer)Fetch into an array where the 1st column is a key and all subsequent columns are valuesPDO::FETCH_CLASSTYPE (integer)PDO::FETCH_SERIALIZE (integer)As PDO::FETCH_INTO but object is provided as a serialized string. Available since PHP 5.1.0.PDO::FETCH_PROPS_LATE (integer)Available since PHP 5.2.0PDO::ATTR_AUTOCOMMIT (integer)If this value is FALSE, PDO attempts to disable autocommit so that the connection begins a transaction.PDO::ATTR_PREFETCH (integer)Setting the prefetch size allows you to balance speed against memory usage for your application. Not all database/driver combinations support setting of the prefetch size. A larger prefetch size results in increased performance at the cost of higher memory usage.PDO::ATTR_TIMEOUT (integer)Sets the timeout value in seconds for communications with the database.PDO::ATTR_ERRMODE (integer)See the Errors and error handling section for more information about this attribute.PDO::ATTR_SERVER_VERSION (integer)This is a read only attribute; it will return information about the version of the database server to which PDO is connected.PDO::ATTR_CLIENT_VERSION (integer)This is a read only attribute; it will return information about the version of the client libraries that the PDO driver is using.PDO::ATTR_SERVER_INFO (integer)This is a read only attribute; it will return some meta information about the database server to which PDO is connected.PDO::ATTR_CONNECTION_STATUS (integer)PDO::ATTR_CASE (integer)Force column names to a specific case specified by the PDO::CASE_* constants.PDO::ATTR_CURSOR_NAME (integer)Get or set the name to use for a cursor. Most useful when using scrollable cursors and positioned updates.PDO::ATTR_CURSOR (integer)Selects the cursor type. PDO currently supports either PDO::CURSOR_FWDONLY and PDO::CURSOR_SCROLL. Stick with PDO::CURSOR_FWDONLY unless you know that you need a scrollable cursor.PDO::ATTR_DRIVER_NAME (string)Returns the name of the driver.
Example #1 using PDO::ATTR_DRIVER_NAME<span style="color: #000000"><font style="background-color: #eeeeee"><span style="color: #0000bb"><?php</span><span style="color: #007700">if (</span><span style="color: #0000bb">$db</span><span style="color: #007700">-></span><span style="color: #0000bb">getAttribute</span><span style="color: #007700">(</span><span style="color: #0000bb">PDO</span><span style="color: #007700">::</span><span style="color: #0000bb">ATTR_DRIVER_NAME</span><span style="color: #007700">) == </span><span style="color: #dd0000">'mysql'</span></font><font style="background-color: #eeeeee"><span style="color: #007700">) {<br />
echo </span><span style="color: #dd0000">"Running on mysql; doing something mysql specific here\n"</span></font><font style="background-color: #eeeeee"><span style="color: #007700">;<br />
}</span><span style="color: #0000bb">?></span> </font></span>
PDO::ATTR_ORACLE_NULLS (integer)Convert empty strings to SQL NULL values on data fetches.PDO::ATTR_PERSISTENT (integer)Request a persistent connection, rather than creating a new connection. See Connections and Connection management for more information on this attribute.PDO::ATTR_STATEMENT_CLASS (integer)PDO::ATTR_FETCH_CATALOG_NAMES (integer)Prepend the containing catalog name to each column name returned in the result set. The catalog name and column name are separated by a decimal (.) character. Support of this attribute is at the driver level; it may not be supported by your driver.PDO::ATTR_FETCH_TABLE_NAMES (integer)Prepend the containing table name to each column name returned in the result set. The table name and column name are separated by a decimal (.) character. Support of this attribute is at the driver level; it may not be supported by your driver.PDO::ATTR_STRINGIFY_FETCHES (integer)PDO::ATTR_MAX_COLUMN_LEN (integer)PDO::ATTR_DEFAULT_FETCH_MODE (integer)Available since PHP 5.2.0PDO::ATTR_EMULATE_PREPARES (integer)Available since PHP 5.1.3.PDO::ERRMODE_SILENT (integer)Do not raise an error or exception if an error occurs. The developer is expected to explicitly check for errors. This is the default mode. See Errors and error handling for more information about this attribute.PDO::ERRMODE_WARNING (integer)Issue a PHP E_WARNING message if an error occurs. See Errors and error handling for more information about this attribute.PDO::ERRMODE_EXCEPTION (integer)Throw a PDOException if an error occurs. See Errors and error handling for more information about this attribute.PDO::CASE_NATURAL (integer)Leave column names as returned by the database driver.PDO::CASE_LOWER (integer)Force column names to lower case.PDO::CASE_UPPER (integer)Force column names to upper case.PDO::NULL_NATURAL (integer)PDO::NULL_EMPTY_STRING (integer)PDO::NULL_TO_STRING (integer)PDO::FETCH_ORI_NEXT (integer)Fetch the next row in the result set. Valid only for scrollable cursors.PDO::FETCH_ORI_PRIOR (integer)Fetch the previous row in the result set. Valid only for scrollable cursors.PDO::FETCH_ORI_FIRST (integer)Fetch the first row in the result set. Valid only for scrollable cursors.PDO::FETCH_ORI_LAST (integer)Fetch the last row in the result set. Valid only for scrollable cursors.PDO::FETCH_ORI_ABS (integer)Fetch the requested row by row number from the result set. Valid only for scrollable cursors.PDO::FETCH_ORI_REL (integer)Fetch the requested row by relative position from the current position of the cursor in the result set. Valid only for scrollable cursors.PDO::CURSOR_FWDONLY (integer)Create a PDOSt
atement object with a forward-only cursor. This is the default cursor choice, as it is the fastest and most common data access pattern in PHP.PDO::CURSOR_SCROLL (integer)Create a PDOStatement object with a scrollable cursor. Pass the PDO::FETCH_ORI_* constants to control the rows fetched from the result set.PDO::ERR_NONE (string)Corresponds to SQLSTATE '00000', meaning that the SQL statement was successfully issued with no errors or warnings. This constant is for your convenience when checking PDO::errorCode() or PDOStatement::errorCode() to determine if an error occurred. You will usually know if this is the case by examining the return code from the method that raised the error condition anyway.PDO::PARAM_EVT_ALLOC (integer)Allocation eventPDO::PARAM_EVT_FREE (integer)Deallocation eventPDO::PARAM_EVT_EXEC_PRE (integer)Event triggered prior to execution of a prepared statement.PDO::PARAM_EVT_EXEC_POST (integer)Event triggered subsequent to execution of a prepared statement.PDO::PARAM_EVT_FETCH_PRE (integer)Event triggered prior to fetching a result from a resultset.PDO::PARAM_EVT_FETCH_POST (integer)Event triggered subsequent to fetching a result from a resultset.PDO::PARAM_EVT_NORMALIZE (integer)Event triggered during bound parameter registration allowing the driver to normalize the parameter name.
php5原来内建的sqlite扩展只支持sqlite2，对sqlite3的支持可以用多种方法实现，我觉得最方便的还是pdo，只需在安装配置php时，设置pdo_sqlite扩展，不需要安装其他的东西。当然功能能也许不及专门的sqlite3扩展。根据官方文档逐渐翻译学习！
http://cn2.php.net/manual/en/intro.pdo.php
PHP Data Objects (PDO)扩展是PHP中一个轻量级的、统一的数据接口。每种数据库依靠特定的正则函数驱动PDO接口，能反映出数据库特征。注意：你不能单独仅依靠PDO扩展来访问任何数据库；你必须使用特定数据库PDO驱动来访问数据库服务器。
PDO提供一个数据访问层，意思是，不管你使用那种数据库，都可以用同样的函数执行查询和获取结果。PDO不提供数据库抽象，如果你需要该功能应该使用成熟的抽象。
PDO是在PHP5.1 中引入，也可以作为PHP5.0的PECL扩展；PDO需要PHP5核心中的新的面现对象特征，所以不能在以前的版本中运行。
The PHP Data Objects (PDO) extension defines a lightweight, consistent interface for accessing databases in PHP. Each database driver that implements the PDO interface can expose database-specific features as regular extension functions. Note that you cannot perform any database functions using the PDO extension by itself; you must use a database-specific PDO driver to access a database server.
PDO provides a data-access abstraction layer, which means that, regardless of which database you're using, you use the same functions to issue queries and fetch data. PDO does not provide a database abstraction; it doesn't rewrite SQL or emulate missing features. You should use a full-blown abstraction layer if you need that facility.
PDO ships with PHP 5.1, and is available as a PECL extension for PHP 5.0; PDO requires the new OO features in the core of PHP 5, and so will not run with earlier versions of PHP.
