PHP and MySQL basic tutorial (3)

The content of this article is about the basic tutorial of PHP and MySQL (3). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Use cookies to track and identify users

Let’s take a look at the content saved in the browser. If you are using IE5, there is a cookies directory in the windows directory. There are many text files in it. The file names are similar to wudong@15seconds[1].txt. These are the cookies used by the browser to save values. . In previous versions of IE, the contents of cookies were viewable, but now the contents are encoded. Before the browser gets a Web page, it will first check whether the domain name of the page exists in the cookie. If there is a match, the browser will first send the matching cookie to the server, and then accept and process the cookie sent by the server. page.

Let’s take an example of cookie application: when I connect to Amazon.com, the browser will send the contents of its previously set cookies to Amazon before accepting the first page. Then Amazon.com checks the content sent to see if there is relevant information in the database. After matching, it creates a customized page for me and sends it over.

Assigning a value to cookies

Cookies must be assigned a value before the server sends any content to the client's browser. To do this, the cookie settings must be placed in the tag:

< ?php 
setcookie("CookieID", $USERID); 
?> 
< HTML> 
< BODY> 
< /BODY> 
< /HTML>

setcookie function has a total of six parameters, separated by commas:

The name of the cookie is a string, for example : "CookieID" . Colons, commas and spaces are not allowed in between. This parameter is required, while all other parameters are optional. If only this parameter is given, the cookie will be deleted.
The value of cookie is usually a string variable, for example: $USERID. You can also assign it a ?? to skip setting the value.
The time when the cookie expires. If omitted (or assigned a value of zero), the cookie will expire at the end of the session. This parameter can be an absolute time, represented by DD-Mon-YY HH:MM:SS, for example: "24-Nov-99 08:26:00". What is more commonly used is to set a relative time. This is achieved through the time() function or the mktime function. For example, time()+3600 will cause the cookie to expire after one hour.
A path used to match cookies. When there are multiple cookie settings with the same name on a server, this parameter is used to avoid confusion. Using the "/" path has the same effect as omitting this parameter. It should be noted that Netscape's cookie definition puts the domain name in front of the path, while PHP does the opposite.
The domain name of the server is also used to match cookies. It should be noted that a dot (.) must be placed before the domain name of the server. For example: ".friendshipcenter.com" . Because unless there are more than two points, this parameter cannot be accepted.
The security level of cookie is an integer. 1 means this cookie can only be sent over "secure" networks. 0 or omitted means any type of network is acceptable.

Cookies and Variables

When the PHP script extracts a cookie from the client's browser, it will automatically convert it into a variable. For example: a cookie named CookieID will become the variable $CookieID. The contents of

Cookies are reported in the HTTP_COOKIE_VARS array. You can also access the specified cookie value through this array and the name of the cookie:

PRint $HTTP_COOKIE_VARS[CookieID];

Remember each user

Look back at the submitform.php3 file above. Its function is to add the customer's name to the database. Now I want to add something to it. I want to assign a unique user ID to each user, and then put this ID in Cookies, so that every time a user visits my website, I can know who he is through the cookie and the user ID in it. .

MySQL can be set to automatically assign a number to each new record. This number starts from 1 and automatically increases by 1 each time thereafter. With one line of SQL statement, you can easily add such a field to the data table. I call it USERID:

ALTER TABLE dbname 
ADD COLUMN 
USERID INT(11) NOT NULL 
PRIMARY KEY AUTO_INCREMENT;

We have made some special settings for this field. First, define its type as an 11-bit integer through "INT(11)"; then use the "NOT NULL" keyword to prevent the value of this field from being NULL; then use "PRIMARY KEY" to set it as an index field, so The search will be faster; finally, "AUTO_INCREMENT" defines it as an automatically incremented field.

After inserting the user’s name into the database, it’s time to set a cookie on their browser. What is used at this time is the value of the USERID field we just talked about:

< ?php 
mysql_connect (localhost, username, passWord); 
mysql_select_db (dbname); 
mysql_query ("INSERT INTO tablename (first_name, last_name) 
VALUES (&#39;$first_name&#39;, &#39;$last_name&#39;) 
"); 
setcookie("CookieID", 
mysql_insert_id(), 
time()+94608000, 
"/"); /* 三年后 cookie 才会失效 */ 
?>

PHP 函数 mysql_insert_id() 返回在最后一次执行了 INSERT 查询后，由 AUTO_INCREMENT 定义的字段的值。这样，只要你不清除掉浏览器的 Cookies ，网站就会永远“记住”你了 

读取 cookie 

我们来写一个像 Amazon.com 所作的那样的脚本。首先， PHP 脚本会先检查客户浏览器是否发送了 cookie 过来，如果是那样的话，用户的姓名就会被显示出来。如果没找到 cookie 的话，就显示一个表单，让客户登记他们的姓名，然后把他添加到数据库中，并在客户浏览其中设置好 cookie 。 

首先，先来显示 cookie 的内容： 

< ?php 
print $CookieID; 
?>

然后，就可以把名字显示出来了： 

< ?php 
mysql_connect (localhost, username, password); 
mysql_select_db (dbname); 
$selectresult = mysql_query ("SELECT * FROM tablename 
WHERE USERID = &#39;$CookieID&#39; 
"); 
$row = mysql_fetch_array($selectresult); 
echo " 欢迎你的光临 ", $row[first_name], "!"; 
?>

就是这样的了。我在其中没有作判断，交给你自己来完成好了 

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 PHP 和 MySQL 基础教程（四）

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