(PHP 5 >= 5.1.0, PHP 7, PECL pdo >= 0.1.0)
PDO::__construct — 创建一个表示数据库连接的 PDO 实例
$dsn
[, string $username
[, string $password
[, array $driver_options
]]] )创建一个表示连接到请求数据库的数据库连接 PDO 实例。
数据源名称或叫做 DSN，包含了请求连接到数据库的信息。
通常，一个 DSN 由 PDO 驱动名、紧随其后的冒号、以及具体 PDO 驱动的连接语法组成。更深入的信息能从 PDO 具体驱动文档找到。
The dsn 参数支持三种不同的方式 创建一个数据库连接：
dsn 包含完整的DSN。
dsn consists of uri:
followed by a URI that defines the location of a file containing
the DSN string. The URI can specify a local file or a remote URL.
uri:file:///path/to/dsnfile
dsn consists of a name
name that maps to
pdo.dsn. in php.ini
defining the DSN string.
name
Note:
别名必须得在 php.ini 中定义了，不能是在 .htaccess 或 httpd.conf 中 。
DSN字符串中的用户名。对于某些PDO驱动，此参数为可选项。
DSN字符串中的密码。对于某些PDO驱动，此参数为可选项。
一个具体驱动的连接选项的键=>值数组。
成功则返回一个PDO对象。
如果试图连接到请求的数据库失败，则PDO::__construct() 抛出一个 PDO异常（PDOException） 。
Example #1 Create a PDO instance via driver invocation
<?php
/* Connect to an ODBC database using driver invocation */
$dsn = 'mysql:dbname=testdb;host=127.0.0.1';
$user = 'dbuser';
$password = 'dbpass';
try {
$dbh = new PDO($dsn, $user, $password);
} catch (PDOException $e) {
echo 'Connection failed: ' . $e->getMessage();
}
?>
Example #2 Create a PDO instance via URI invocation
The following example assumes that the file /usr/local/dbconnect exists with file permissions that enable PHP to read the file. The file contains the PDO DSN to connect to a DB2 database through the PDO_ODBC driver:
odbc:DSN=SAMPLE;UID=john;PWD=mypass
The PHP script can then create a database connection by simply passing the uri: parameter and pointing to the file URI:
<?php
/* Connect to an ODBC database using driver invocation */
$dsn = 'uri:file:///usr/local/dbconnect';
$user = '';
$password = '';
try {
$dbh = new PDO($dsn, $user, $password);
} catch (PDOException $e) {
echo 'Connection failed: ' . $e->getMessage();
}
?>
Example #3 使用别名创建一个PDO实例
The following example assumes that php.ini contains the following entry to enable a connection to a MySQL database using only the alias mydb:
[PDO] pdo.dsn.mydb="mysql:dbname=testdb;host=localhost"
<?php
/* 使用别名连接到一个ODBC数据库 */
$dsn = 'mydb';
$user = '';
$password = '';
try {
$dbh = new PDO($dsn, $user, $password);
} catch (PDOException $e) {
echo 'Connection failed: ' . $e->getMessage();
}
?>
Just to give an odbc string connection example to MSSQL:
$odbc="odbc:Driver={SQL Server};Server=$server;Database=$database;";
$cnx = new PDO( $odbc , $user, $password);
$sql="SELECT field FROM Quotation_Header WHERE (field> 0)";
foreach ($cnx->query($sql) as $row) {
echo $row['field'] . "\n";
}
For IBM i / iSeries / AS400 DB2 connections, you can specify system naming and library lists for php_pdo modules > 1.3.3-sg2
<?php
$pdo = new PDO(
'ibm:' . $host,
$user,
$password,
array(
PDO::I5_ATTR_DBC_SYS_NAMING => true,
PDO::I5_ATTR_DBC_LIBL => "QGPL QSYS"
)
);
?>
See http://yips.idevcloud.com/wiki/index.php/XMLSERVICE/PHPPDOChangeLog
The PDO connection is case-sensitive, this means that you cannot write
`$PDO = new PDO("MySQL:DBName=dbname;host=localhost");`
You would have to write it
`$PDO = new PDO("mysql:dbname=dbname;host=localhost");`
The difference here is that `mysql` and `dbname` is with all lower-case.
Some IDE's like PHPStorm will show a `TYPO ERROR`, at `dbname` if it's written with lower-case only, this is just to be ignored and have been reported to PHPStorm for them to fix. (Currrent version 10.0.2)
You will get a fatal error if you don't catch the exception threw by PDO when it fails to connect to the database server like this.
Fatal error: in xxx.php on line xx
This error neither can be handled by error handlers nor can it be erased by the @ sign, which can make your script uncontrollable.
<?php
$db = new pdo('mysql:host=127.0.0.1;port=3306;dbname=mysql;charset=utf8','user','password',array(
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
));
?>
You should always try ... catch ...
<?php
try{
$db = new pdo('mysql:host=127.0.0.1;port=3306;dbname=mysql;charset=utf8','user','password',array(
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
));
}catch(PDOException $pe){
echo $pe->getMessage();
}
?>
I'd like to point out that in PHP 7.0 in the dsn parameter you can't use 'host=localhost' to solve this you can use 'host=127.0.0.1' instead.
If you happen to create a dsn like this...
<?php
//wrong dsn
$db = new PDO('mysql:database=yourdb;host=127.0.0.1', 'user', 'password');
$stmt = $db->prepare('SELECT * FROM tbl WHERE id = :id');
$stmt->bindParam(':id', $user_id, PDO::PARAM_INT);
$result = $stmt->execute();
?>
... your result will be bool(false) and your $db->errorInfo() will be "0000" which isn't very helpful.
You have to look to the $stmt->errorInfo() to see "No database selected" which is even more confusing until you realize that it's not 'database' but 'dbname' in your DSN! You would think the error about a bad DSN would be in the $db errorInfo but it is not, it's not until you try the $stmt that the error is generated.
<?php
//correct dsn
$db = new PDO('mysql:dbname=yourdb;host=127.0.0.1', 'user', 'password');
?>
I wasted a half hour on that one.
Although not explicitly stated, parameters in the PDO $dsn string may be case-sensitive on some platforms or drivers.
<?php
// The dbname will not be parsed with incorrect casing:
$pdo = new PDO("mysql:host=hostname;DBName=database", "user", "password");
// The correct dbname is lowercase, as displayed in the manual:
$pdo = new PDO("mysql:host=hostname;dbname=database", "user", "password");
?>
To connect to the database via a function use this and call the getConnection function in the class constructor.
<?php
class Connection{
protected $db;
public function Connection(){
$conn = NULL;
try{
$conn = new PDO("mysql:host=localhost;dbname=dbname", "dbuser", "dbpass");
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch(PDOException $e){
echo 'ERROR: ' . $e->getMessage();
}
$this->db = $conn;
}
public function getConnection(){
return $this->db;
}
}
?>
To get UTF-8 charset you can specify that in the DSN.
$link = new PDO("mysql:host=localhost;dbname=DB;charset=UTF8");
Sqlite:
<?php
try{
$pdo = new PDO('sqlite:example.db');
}catch (PDOException $e){
die ('DB Error');
}
?>
If 'example.db' does not exist, no exception is thrown but the file 'example.db' is created.
To connect throught unix socket you need to use
<?php
$dsn = 'mysql:dbname=testdb;unix_socket=/path/to/socket';
?>
You musn't specify host when using socket.
If you use the UTF-8 encoding, you have to use the fourth parameter :
<?php
$db = new PDO('mysql:host=myhost;dbname=mydb', 'login', 'password', array(PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES \'UTF8\''));
?>
To specify a database connection port use the following DSN string
<?php
$dsn = 'mysql:dbname=testdb;host=127.0.0.1;port=3333';
?>