Summary of some understanding of PHP PDO, summary of phppdo_PHP tutorial

Summary of some understanding of PHP PDO, summary of phppdo

1. The PDO (PHP Data Object) extension defines a lightweight, persistent interface for PHP to access the database. Each database driver that implements the PDO interface can express its own characteristics in the form of regular expansion.

Mainly: PDO extension is just an abstract interface layer. The PDO extension itself cannot implement any database operations. A specific database PDO driver must be used to access the database

2. Start PDO method : Find the php.ini file

Copy code The code is as follows:

;extension=php_pdo.dll

Just remove the preceding semicolon (similar in Linux environment)

3. PDO predefined class:

PDO contains three predefined classes: PDO, PDOStatement, PDOException

(1) PDO class: represents a connection between PHP and database

PDO: Constructor, creates a new PDO object

　beginTransaction：Start transaction

Commit: Submit transaction

errorCode: Return an error code from the database, if any

errorInfo: Returns an array containing error information from the database, if any

Exec: Execute a SQL statement and return the number of affected rows

GetAttribute: Returns a database connection attribute

LastInsertId: Returns the latest row (ID) inserted into the database

Prepare: Prepare a SQL statement for execution and return the joint result set after the statement is executed

Query: execute a SQL statement and return a result set

rollBack: roll back a transaction

SetAttribute: Set a database connection attribute

(2) PDOStatement class: represents a preprocessing statement and the joint result set after the statement is executed

bindColomn: Bind a PHP variable to the result set output column

bindParam: Bind a variable to a parameter in a PHP prepared statement

bindValue: Bind a value to the parameter in the processing statement

closeCursor: Close the cursor so that the statement can be executed again

cloumnCount: Returns the number of columns in the result set

ErrorCode: Return an error code from the statement, if any

errorInfo: Returns an array containing error information from the statement

execute: execute a prepared statement

fetch: Fetch a row from the result set

fetchAll: Get an array containing all rows from the result set

fetchColomn: Returns the data of a certain column in the result set

GetAttribute: Returns a PDOStatement attribute

GetColomnMeta: Returns the structure of a column in the result set

NextRowset: Returns the next result set

RowCount: Returns the number of rows affected after the SQL statement is executed

SetAttribute: Set a PDOStatement attribute

SetFetchMode: Set to get data for PDOStatement

Give a simple example of transaction processing:

Copy code The code is as follows:

/*
Transaction processing
        MYSQL table engine MyISAM InnoDB
           Add fields alter table user add money int not null default 0;
View table engine show create table user
Modify table engine alter table user engine=InnoDB
*/

       
Try{
​​​​ //Instantiate PDO
          $pdo=new PDO("mysql:host=localhost;dbname=photo","root","123456".array('3'=>'2'));
}catch(PDOException $e){
echo $e->getMessage();
}
//Set character set
$sql="set name utf8";
$pdo->exec($sql);
//Start transaction processing
$pdo->beginTransaction();
$num=250;
$sql="update user set money=money-{$num} where id =1";
$rows=$pdo->exec($sql);
       
$sql="update user set monet=money-{$num} where id=2";
$rows+=$pdo->exec($sql);
//End transaction processing
If($rows==2){
          $pdo->commit();
}else{
          $pdo->rollBack();
}
?>

(Main characteristics of transactions: atomicity, consistency, independence and durability)

4. The biggest feature of PDO is the introduction of parameter binding and pre-compilation

Pre-compilation is responsible for two things, transfer and soft parsing speed. To support pre-compilation, in addition to database support, the program also needs driver support (PDO and NySQLi support)

5. PDO efficiency issues

(1) Tested on a large table with large data volume, PDO’s CRUD efficiency is 5%~15% lower than MySql direct connection, and the variance is greater than MySQL direct connection

(2) As for the load, after PDO opens a long connection, the load is higher than MySQL and relatively stable.

In fact, in actual applications, 90% of programs do not perform database migration, and there are very few applications that do database migration.

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