[PHP foundation] realize the connection between PHP and SQL database

1 Preface

1. In order to realize the function of web page accessing background database , You need to connect it with the corresponding database in the web page code .
2. PHP 5 And above, we recommend the following ways to connect MySQL :
   1. MySQLi extension (“i” Meaning for improved).
   2. PDO (PHP Data Objects).
3. Comparison of two connection modes ：
   1. PDO Apply to 12 In different databases , MySQLi Only aim at MySQL database .
   2. If the project needs to switch between multiple databases , It is recommended to use PDO , In this way, you only need to modify the connection string and some query statements . If you use MySQLi Connecting to different databases , You need to rewrite all the code , Including inquiries .
   3. Both are object-oriented , but MySQLi It also provides API Interface .
   4. Both support preprocessing statements . Preprocessing statements can prevent SQL Inject , about web The security of the project is very important .
4. This section introduces the implementation of PHP And SQL The whole process of connection , This paper mainly introduces MySQLi Method .

2 Realization PHP Connect SQL The whole process of database experiment

2.1 Experimental environment

1. Server side ： This experiment is based on virtual machine win2008 Systematic WAMP Environment , Refer to the article for the configuration process related to this environment 《win2008R2SP1+WAMP The deployment environment 》.
2. client ： Use the browser to access and control .
3. The server and the client are under the same LAN , Open the server phpstudy And make sure you can access... From the client browser .

2.2 Create database

1. Log in through the browser on the client phpMyAdmin, The location is located in... Under the default root directory of the website phpMyAdmin Under the folder , Enter the target in the browser “IP+/phpMyAdmin” Visit , The default account passwords are root.
   
2. After logging in, you can see the following interface , On the left is the default 4 A database . Click the database shown by the arrow , Get into .
   
3. Create a new learning test database , Name it my_test, Type selection is “utf8_genrral_ci”, Click Create .
   
4. Once created , You can see the created database here on the left . Click the database to enter .
   
5. After entering, you can see that there are no forms in the database .
   
6. Create a data table , Name it users, It is mainly used to store user information （id name password photo money） common 5 A field . Enter the following information and click execute .
   
7. Create these fields ,id name password photo money, And set the type and length of the response , take id Set key as primary key .（ The primary key must be non empty ）.
   
8. You can click on the left side to create a new users surface , The detailed structure information of this table is shown in the figure below .
   

2.3 insert data

1. Click on SQL Enter the table modification interface , available SQL Statement execution .
   
2. Modify the command as follows and click execute . Note that the symbol is in English format .

INSERT INTO `users`( `name`, `password`,`photo`, `money`) VALUES ("libai",123456,"./touxiang.jpg",100);
INSERT INTO `users`( `name`, `password`,`photo`, `money`) VALUES (" Li Bai ",123456,"./touxiang.jpg",100);

3. Click on the left users surface , You can see the user information we entered . Here we enter libai And Li Bai , As shown in the figure below .
   

2.4 Realization PHP Interacting with the database

2.4.1 Realization PHP Interact with the database in three steps

1.  Establishing a connection . When a user establishes a connection , You need to provide a user name + password + Address + Database name , The database name can be switched during connection .
2.  perform SQL sentence . 
3.  disconnect .

2.4.2 Code 1 ： Simple implementation of three steps

Simply realize the three steps of interaction , And feedback information according to whether the connection is successfully established . Visit this page to get the results

<?php
$dbHost = "127.0.0.1";	// Database address 
$dbUser = "root";		// The direct assignment here is root, The actual use should be that the user logs in and enters his own account .
$dbPass = "root";		// The direct assignment here is root, The actual use should be that the user logs in and enters his own password .
$dbName = "my_test";
$link = @mysqli_connect($$dbHost,$dbUser,$dbPass,$dbName);// Establishing a connection , No display notice Information 
if (!$link)
	{
    echo mysqli_connect_error();}		// If the connection cannot be established, an error message is displayed .
$sql = "select * from users";			// Define the statement to execute .
$results = mysqli_query($link,$sql);	// Execute the statement to get data from the connection .
var_dump($results);						// Check the type of data obtained .
// The output of web pages is object type ：object(mysqli_result)#2 (5) { ["current_field"]=> int(0) ["field_count"]=> int(5) ["lengths"]=> NULL ["num_rows"]=> int(2) ["type"]=> int(0) }
mysqli_close($link);					// disconnect 
?>

2.4.3 Code 2 ： Optimize code one

Based on code one , Get the data branch execution according to whether the statement is successfully executed , If successful, print the obtained data information in turn , If yes, an error prompt will be displayed . The result of browser access code 2 is shown in Figure , Among them, Chinese is garbled .

<?php
$dbHost = "127.0.0.1";
$dbUser = "root";
$dbPass = "root";
$dbName = "my_test";
$link = @mysqli_connect($$dbHost,$dbUser,$dbPass,$dbName);
if (!$link)
	{
    echo mysqli_connect_error();}
$sql = "select * from users";
if ($results = mysqli_query($link,$sql)){
    			//mysqli_query When the function fails to execute, it returns  false, adopt mysqli_query()  Successful execution SELECT, SHOW, DESCRIBE or  EXPLAIN The query will return a mysqli_result  object , Other queries return true.
	while ($result = mysqli_fetch_assoc($results)){
    	// Use mysqli_fetch_assoc Function to get the specific data in the return object .
		var_dump($result);
		echo "<hr/>";
	}
}
else{
    
	die(mysqli_error($link));
}
mysqli_close($link);
?>

2.4.4 Code three ： Change the connection mode to object-oriented

The main difference between object-oriented connection and process oriented in code one and two is , Connection process 、 The judgment process 、 The difference in the disconnection process . The process of data access and use is basically the same .

<?php
$dbHost = "127.0.0.1";
$dbUser = "root";
$dbPass = "root";
$dbName = "my_test";
$link = @new mysqli($$dbHost,$dbUser,$dbPass,$dbName);
if ($link->connect_error)	
	{
    echo $mysqli->connect_error;}
$sql = "select * from users";
if ($results = mysqli_query($link,$sql)){
    			//mysqli_query When the function fails to execute, it returns  false, adopt mysqli_query()  Successful execution SELECT, SHOW, DESCRIBE or  EXPLAIN The query will return a mysqli_result  object , Other queries return true.
	while ($result = mysqli_fetch_assoc($results)){
    	// Use mysqli_fetch_assoc Function to get the specific data in the return object .
		var_dump($result);
		echo "<hr/>";
	}
}
else{
    
	die(mysqli_error($link));
}
$link->close();
?>

3 Introduction to correlation function

3.1 Database connection operation related functions

Function name	effect
new mysqli() mysqli_connect()	Connect to the specified database
$mysqli->connect_errno mysqli_connect_errno()	Return the error code of the last connection call
$mysqli->connect_error mysqli_connect_error()	Returns the error code of the last connection call described by a string
$link->close() mysqli_close($link)	disconnect , among $link Indicates the established connection .

3.2 Operation result set object correlation function

function	effect
mysqli_fetch_row()	Get the data of a record by index array
mysqli_fetch_assoc()	Get the data of a record in the way of associative array
mysqli_fetch_array()	Get the data of a record by indexing array or associative array
mysqli_fetch_all()	Get the data of all records by indexing the genus pig or associative array
mysqli_num_rows()	Get the number of rows in the result
mysqli_free_result()	Freeing memory associated with a result set

3.3 More orders

For more orders, please refer to the official manual 《MySQL Enhanced extensions 》.

4 summary

1. master phpstudy Operation mode of database in ;
2. master PHP And MySQL Database connection and use ;
3. Master common commands ;
4. Understand the differences between object-oriented and process oriented connection ;
5. Understand the general content of the official manual .