Detailed explanation of usage of php pdo function library

pdo->begintransaction() — Mark the starting point of rollback
pdo->commit() — Mark the end point of rollback and execute sql
pdo->__construct() — Establish a pdo link database Example of
pdo->errorcode() — Get error code
pdo->errorinfo() — Get error information
pdo->exec() — Process a sql statement and return the number of entries affected
pdo ->getattribute() — Get the attributes of a "database connection object"
pdo->getavailabledrivers() — Get the valid pdo driver name
pdo->lastinsertid() — Get the primary key of the last piece of data written Value
pdo->prepare() — Generate a "query object"
pdo->query() — Process a sql statement and return a "pdostatement"
pdo->quote() — For a certain sql Add quotes to the string
pdo->rollback() — perform rollback
pdo->setattribute() — set attributes for a "database connection object"

2. pdostatement

pdostatement->bindcolumn() — bind a column to a php variable
pdostatement->bindparam() — binds a parameter to the specified variable name
pdostatement->bindvalue() — binds a value to a parameter
pdostatement->closecursor() — closes the cursor, enabling the statement to be executed again.
pdostatement->columncount() — returns the number of columns in the result set
pdostatement->errorcode() — fetch the sqlstate associated with the last operation on the statement handle
pdostatement->errorinfo() — fetch extended error information associated with the last operation on the statement handle
pdostatement->execute() — executes a prepared statement
pdostatement ->fetch() — fetches the next row from a result set
pdostatement->fetchall() — returns an array containing all of the result set rows
pdostatement->fetchcolumn() — returns a single column from the next row of a result set
pdostatement->fetchobject() — fetches the next row and returns it as an object.
pdostatement->getattribute() — retrieve a statement attribute
pdostatement->getcolumnmeta() — returns metadata for a column in a result set
pdostatement->nextrowset() — advances to the next rowset in a multi-rowset statement handle
pdostatement->rowcount() — returns the number of rows affected by the last sql statement
pdostatement- >setattribute() — set a statement attribute
pdostatement->setfetchmode() — set the default fetch mode for this statement

Detailed explanation 1) Database connection in pdo

$dsn = 'mysql:dbname=ent;host=127.0.0.1′;
$user = 'root';
$password = '123456';
try {
$dbh = new pdo($ dsn, $user, $password, array(pdo::attr_persistent => true));
$dbh->query('set names utf8;');
foreach ($dbh->query('select * from tpm_juese') as $row) {
print_r($row);
}
} catch (pdoexception $e) {
echo 'connection failed: ' . $e->getmessage();
}

Many web applications will be optimized by using persistent connections to the database. Persistent connections are not closed at the end of the script, Instead it is cached and reused when another script requests a connection with the same ID. The cache of persistent connections allows you to avoid the resource consumption of deploying a new connection every time the script needs to talk to the database, making your web application faster. The array(pdo::attr_persistent => true) in the above example sets the connection type to a persistent connection.

Detailed explanation 2) Transactions in pdo The three methods pdo->begintransaction(), pdo->commit(), and pdo->rollback() are used together when the rollback function is supported. The pdo->begintransaction() method marks the starting point, the pdo->commit() method marks the rollback end point and executes sql, and pdo->rollback() performs rollback.

try {
$dbh = new pdo('mysql:host=localhost;dbname=test', 'root', ”);
$dbh->query('set names utf8;');
$dbh->setattribute(pdo::attr_errmode, pdo::errmode_exception);
$dbh->begintransaction();
$dbh->exec(”insert into `test`.` table` (`name` ,`age`)values ​​('mick', 22);”);
$dbh->exec(”insert into `test`.`table` (`name` ,`age`) values ​​('lily', 29);");
$dbh->exec("insert into `test`.`table` (`name` ,`age`)values ​​('susan', 21);") ;
$dbh->commit();
} catch (exception $e) {
$dbh->rollback();
echo “failed: ” . $e->getmessage();
}
? >

Now that the connection has been established through pdo, you must understand how pdo manages transactions before deploying the query. If you have never encountered transaction processing before, (now a brief introduction. :) They provide 4 main features: atomicity, consistency, isolation and durability (acid). In layman's terms, all the work in a transaction is committed when it is committed, even if it is It is executed in stages and must be applied safely to the database without being interfered by other connections. The transaction work can also be easily canceled automatically when an error occurs in the request.

The typical use of transactions is to "save" batch changes and then execute them immediately. This will have the benefit of completely improving update efficiency. In other words, transactions can make your scripts faster and potentially more robust (you still need to use them correctly to realize this benefit).

Unfortunately, not every database supports transactions, so pdo needs to be running in what is considered "autocommit" mode when the connection is established. Autocommit mode means that every query you execute has its own implicit transaction processing, whether the database supports transactions or there is no transaction because the database does not support it. If you need a transaction, you must create one using the pdo->begintransaction() method. If the underlying driver does not support transactions, a pdoexception will be thrown (regardless of your exception handling settings, since this is always a serious error condition). Within a transaction, you can end it using pdo->commit() or pdo->rollback(), depending on whether the code in the transaction ran successfully. When the script ends or a connection is closed, if you have an unfinished transaction, pdo will automatically roll it back. This is a safe solution in case the script terminates unexpectedly - if you don't explicitly commit the transaction, it will assume that something went wrong and perform a rollback for the safety of your data.

2. pdostatement

// Modify the default error display level
$dbh->setattribute(pdo::attr_errmode, pdo::errmode_warning);
?>