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原文：Getting PHP to Talk to MySQlNow that youre comfortable using the MySQL client tools to manipulate data in the database, you can begin using PHP to display and modify data from the database. PHP has standard functions for working with the database.First, were going to discuss PHPs built-in database functions. Well also show you how to use the The PHP Extension and Application Repository (PEAR) databasefunctions that provide the ability to use the same functions to access any supported database. This type of flexibility comes from a process called abstraction. In programming interfaces, abstraction simplifies a complex interaction. It works byremoving any nonessential parts of the interaction, allowing you to concentrate on the important parts. PEARs DB classes are one such database interface abstraction. The information you need to log into a database is reduced to the bare minimum. This standard format allows you to interact with MySQL, as well as other databases using the same functions. Similarly, other MySQL-specific functions are replaced with generic ones that know how to talk to many databases. For example, the MySQL-specific connect function is:mysql_connect($db_host, $db_username, $db_password);versus PEARs DB connect function:$connection = DB:connect(mysql:/$db_username:$db_password$db_host/$db_database);The same basic information is present in both commands, but the PEAR function also specifies the type of databases to which to connect. You can connect to MySQL or other supported databases. Well discuss both connection methods in detail.In this chapter, youll learn how to connect to a MySQL server fromPHP, how to use PHP to access and retrieve stored data, and how to correctly display information to the user.The ProcessThe basic steps of performing a query, whether using the mysql command-line tool or PHP, are the same: Connect to the database. Select the database to use. Build a SELECT statement. Perform the query. Display the results.Well walk through each of these steps for both plain PHP and PEAR functions.ResourcesWhen connecting to a MySQL database, you will use two new resources. The first is the link identifier that holds all of the information necessary to connect to the database for an active connection. The other resource is the results resource. It contains all information required to retrieve results from an active database querys result set. Youll be creating and assigning both resources in this chapter.Querying the Database with PHP FunctionsIn this section, we introduce how to connect to a MySQL database with PHP. Its quite simple, and well begin shortly with examples, but we should talk briefly about what actually happens. When you try connecting to a MySQL database, the MySQL server authenticates you based on your username and password. PHP handles connectingto the database for you, and it allows you to start performing queries and gathering data immediately.As in Chapter 8, well need the same pieces of information to connect to the database: The IP address of the database server The name of the database The username The passwordBefore moving on, make sure you can log into your database using the MySQL command-line client.Figure 9-1 shows how the steps of the database interaction relate to the two types of resources. Building the SELECT statement happens before the third function call, but it is not shown. Its done with plain PHP code, not a MySQL-specific PHP function.Figure 9-1. The interaction between functions and resources when using the databaseIncluding Database Login DetailsYoure going to create a file to hold the information for logging into MySQL. Storing this information in a file you include is recommended. If you change the database password, there is only one place that you need to change it, regardless of how manyPHP files you have that access the database.You dont have to worry about anyone directly viewing the file and getting your database login details. The file, if requested by itself, is processed as a PHP file and returns a blank page.Troubleshooting connection errorsOne error you may get is:Fatal error: Call to undefined function mysql_connect( ) in C:Program FilesApacheSoftware FoundationApache2.2htdocsdb_test.php on line 4This error occurs because PHP 5.x for Windows was downloaded, and MySQL support was not included by default. To fix this error, copy the php_mysql.dll file from the ext/ directory of the PHP ZIP file to C:php, and then C:WINDOWSphp.ini.Make sure there are two lines that are not commented out by a semicolon (;) at the beginning of the line like these:extension_dir = c:/PHP/ext/extension=php_mysql.dllThis will change the extension to include the directory to C:/php and include the MySQL extension, respectively. You can use the Search function of your text editor to check whether the lines are already there and just need to be uncommented, or whether they need to be added completely.Youll need to restart Apache, and then MySQL support will be enabled.Selecting the DatabaseNow that youre connected, the next step is to select which database to use with the mysql_select_db command. It takes two parameters: the database name and, optionally, the database connection. If you dont specify the database connection, the default is the connection from the last mysql_connect:/ Select the database$db_select=mysql_select_db($db_database);if (!$db_select)die (Could not select the database: . mysql_error( );Again, its good practice to check for an error and display it every time you access the database.Now that youve got a good database connection, youre ready to execute your SQL query.Building the SQL SELECT QueryBuilding a SQL query is as easy as setting a variable to the string that is your SQL query. Of course, youll need to use a valid SQL query, or MySQL returns with an error when you execute the query. The variable name $query is used since the name reflects its purpose, but you can choose anything youd like for a variable name. The SQL query in this example is SELECT * FROM books.You can build up your query in parts using the string concatenate (.) operator:Executing the QueryTo have the database execute the query, use the mysql_query function. It takes two parametersthe query and, optionally, the database linkand returns the result. Save a link to the results in a variable called, you guessed it, $result! This is also a good place to check the return code from mysql_query to make sure that there were no errors in the query string or the database connection by verifying that $result is not FALSE:When the database executes the query, all of the results forma result set. These results correspond to the rows that you saw upon doing a query using the mysql command-line client. To display them, you process each row, one at a time.Fetching and DisplayingUse mysql_fetch_row to get the rows from the result set. Its syntax is:array mysql_fetch_row ( resource $result);It takes the result you stored in $result fromthe query as a parameter. It returns one row at a time from the query until there are no more rows, and then it returns FALSE. Therefore, you do a loop on the result of mysql_fetch_row and define some code to display each row:The columns of the result row are stored in the array and can be accessed one at a time. The variable $result_row2 accesses the second attribute (as defined in the querys column order or the column order of the table if SELECT * is used) in the result row.Fetch typesThis is not the only way to fetch the results. Using mysql_fetch_array, PHP can place the results into an array in one step. It takes a result as its first parameter, and the way to bind the results as an optional second parameter. If MYSQL_ASSOC is specified, the results are indexed in an array based on their column names in the query. If MYSQL_NUM is specified, then the number starting at zero accesses the results. The default value, MYSQL_BOTH, returns a result array with both types. The mysql_fetch_assoc is an alternative to supplying the MYSQL_ASSOC argument.Closing the ConnectionAs a rule of thumb, you always want to close a connection to a database when youredone using it. Closing a database with mysql_close will tell PHP and MySQL that you no longer will be using the connection, and will free any resources and memory allocated to it:mysql_close($connection)InstallingPEAR uses a Package Manager that oversees which PEAR features you install.Whether you need to install the Package Manager depends on which version of PHP you installed. If youre running PHP 4.3.0 or newer, its already installed. If yourerunning PHP 5.0, PEAR has been split out into a separate package. The DB package that youre interested in is optional but installed by default with the Package Manager. So if you have the Package Manager, youre all set.UnixYou can install the Package Manager on a Unix systemby executing the followingfrom the shell (command-line) prompt:lynx -source / | phpThis takes the output of the site (which is actually the source PHP code) to install PEAR and passes it along to the php command for execution.WindowsThe PHP 5 installation includes the PEAR installation script as C:phpgo-pear.bat. In case you didnt install all the files in Chapter 2, go ahead and extract all the PHP files to C:/php from the command prompt, and execute the .bat file.Creating a connect instanceThe DB.php file defines a class of type DB. Refer to Chapter 5 for more information on working with classes and objects. Well principally be calling the methods in the class. The DB class has a connect method, which well use instead of our old connect function, mysql_connect. The double colons (:) indicate that were calling that function from the class in line 4:$connection = DB:connect(mysql:/$db_username:$db_password$db_host/$db_database);When you call the connect function, it creates a new database connection that is stored in the variable $connection. The connect function attempts to connect to the database based on the connect string you passed to it.Connect stringThe connect string uses this new format to represent the login information that you already supplied in separate fields:dbtype:/username:passwordhost/databaseThis format may look familiar to you, as its very similar to the connect string for a Windows file share. The first part of the string is what really sets the PEAR functions apart fromthe plain PHP. The phptype field specifies the type of database to connect. Supported databases include ibase, msql, mssql, mysql, oci8, odbc, pgsql, and sybase. All thats required for your PHP page to work with a different type of database is changing the phptype!The username, password, host, and database should be familiar from the basic PHP connect. Only the type of connection is required. However, youll usually want to specify all fields.After the values from db_login.php are included, the connect string looks like the following:mysql:/test:testlocalhost/testIf the connect method on line 6 was successful, a DB object is created. It contains the methods to access the database as well as all of the information about the state of that database connection.QueryingOne of the methods it contains is called query. The query method works just like PHPs query function in that it takes a SQL statement. The difference is that the arrow syntax (-) is used to call it fromthe object. It also returns the results as another object instead of a result set:$query = SELECT * FROM books$result = $connection-query($query);Based on the SQL query, this code calls the query function fromthe connectionobject and returns a result object named $result.FetchingLine 22 uses the result object to call the fetchRow method. It returns the rows one at a time, similar to mysql_fetch_row:while ($result_row = $result-fetchRow( ) echo Title: .$result_row1 . ;echo Author: .$result_row4 . ;echo Pages: .$result_row2 . ;Use another while loop to go through each row from fetchRow until it returns FALSE. The code in the loop hasnt changed from the non-PEAR example.ClosingYoure finished with the database connection, so close it using the object method disconnect:$connection-disconnect( );PEAR error reportingThe function DB:isError will check to see whether the result thats been returned to you is an error. If it is an error, you can use DB:errorMessage to return a text description of the error that was generated. You need to pass DB:errorMessage, the return value from your function, as an argument.Here you rewrite the PEAR code to use error checking:query( $sql)echo DB:errorMessage($demoResult); elsewhile ($demoRow = $demoResult-fetchRow( )echo $demoRow2 . ;?Theres also a new version of the PEAR database interface called PEAR:MDB2. The same results display, but there are more functions available in this version of the PEAR database abstraction layer.Now that you have a good handle on connecting to the database and the various functions of PEAR。譯文：通過(guò)PHP訪問(wèn)MySQL現(xiàn)在你已經(jīng)可以熟練地使用MySQL客戶端軟件來(lái)操作數(shù)據(jù)庫(kù)里的數(shù)據(jù)，我們也可以開始學(xué)習(xí)如何使用PHP來(lái)顯示和修改數(shù)據(jù)庫(kù)里的數(shù)據(jù)了。PHP有標(biāo)準(zhǔn)的函數(shù)用來(lái)操作數(shù)據(jù)庫(kù)。我們首先學(xué)習(xí)PHP內(nèi)建的數(shù)據(jù)庫(kù)函數(shù)，然后會(huì)學(xué)習(xí)PHP擴(kuò)展和應(yīng)用程序庫(kù)（PEAR，PHP Extension and Application Repository ）中的數(shù)據(jù)庫(kù)函數(shù)，我們可以使用這些函數(shù)操作所有支持的數(shù)據(jù)庫(kù)。這種靈活性源自于抽象。對(duì)于編程接口而言，抽象簡(jiǎn)化了復(fù)雜的交互過(guò)程。它將交互過(guò)程中無(wú)關(guān)緊要的部分屏蔽起來(lái)，讓你關(guān)注于重要的部分。PEAR的DB類就是這樣一種數(shù)據(jù)庫(kù)接口的抽象。你登錄一個(gè)數(shù)據(jù)庫(kù)所需要提供的信息被減少到最少。這種標(biāo)準(zhǔn)的格式可以通過(guò)同一個(gè)函數(shù)來(lái)訪問(wèn)MySQL以及其他的數(shù)據(jù)庫(kù)。同樣，一些MySQL特定的函數(shù)被更一般的、可以用在很多數(shù)據(jù)庫(kù)上的函數(shù)所替代。比如，MySQL特定的連接函數(shù)是： mysql_connect($db_host, $db_username, $db_password);而PEAR的DB提供的連接函數(shù)是：$connection = DB:connect(mysql:/$db_username:$db_password$db_host/$db_database);兩個(gè)命令都提供了同樣的基本信息，但是PEAR的函數(shù)中還指定了要連接的數(shù)據(jù)庫(kù)的類型。你可以連接到MySQL或者其他支持的數(shù)據(jù)庫(kù)。我們會(huì)詳細(xì)討論這兩種連接方式。本章中，我們會(huì)學(xué)習(xí)如何從PHP連接到MySQL的服務(wù)器，如何使用PHP訪問(wèn)數(shù)據(jù)庫(kù)中存儲(chǔ)的數(shù)據(jù)，以及如何正確的向用戶顯示信息。步驟無(wú)論是通過(guò)MySQL命令行工具，還是通過(guò)PHP，執(zhí)行一個(gè)查詢的基本步驟都是一樣的： 連接到數(shù)據(jù)庫(kù) 選擇要使用的數(shù)據(jù)庫(kù) 創(chuàng)建SELECT語(yǔ)句 執(zhí)行查詢 顯示結(jié)果我們將逐一介紹如何用PHP和PEAR的函數(shù)完成上面的每一步。資源當(dāng)連接到MySQL數(shù)據(jù)庫(kù)的時(shí)候，你會(huì)使用到兩個(gè)新的資源。第一個(gè)是連接的標(biāo)識(shí)符，它記錄了一個(gè)活動(dòng)連接用來(lái)連接到數(shù)據(jù)庫(kù)所必需的所有信息。另外一個(gè)資源是結(jié)果資源，它包含了用來(lái)從一個(gè)有效的數(shù)據(jù)庫(kù)查詢結(jié)果中取出結(jié)果所需要的所有信息。本章中我們會(huì)創(chuàng)建并使用這兩種資源。使用PHP函數(shù)查詢數(shù)據(jù)庫(kù)本節(jié)我們會(huì)介紹如何使用PHP連接MySQL數(shù)據(jù)庫(kù)。這非常簡(jiǎn)單，我們會(huì)用一些例子說(shuō)明。但是之前我們應(yīng)該稍微了解一下幕后發(fā)生的事情。當(dāng)你試圖連接一個(gè)MySQL數(shù)據(jù)庫(kù)的時(shí)候，MySQL服務(wù)器會(huì)根據(jù)你的用戶名和密碼進(jìn)行身份認(rèn)證。PHP為你建立數(shù)據(jù)庫(kù)的連接，你可以立即開始查詢并得到結(jié)果。我們需要同樣的信息來(lái)連接數(shù)據(jù)庫(kù)： 數(shù)據(jù)庫(kù)服務(wù)器的IP地址 數(shù)據(jù)庫(kù)的名字 用戶名 密碼在開始之前，首先使用MySQL的命令行客戶端確認(rèn)你登錄到數(shù)據(jù)庫(kù)。圖9-1顯示了數(shù)據(jù)庫(kù)交互過(guò)程的各個(gè)步驟和兩種類型資源之間的關(guān)系。創(chuàng)建SELECT語(yǔ)句發(fā)生在第三個(gè)函數(shù)調(diào)用之前，但是在圖中沒(méi)有顯示出來(lái)。它是通過(guò)普通的PHP代碼，而不是MySQL特定的PHP函數(shù)完成的。圖9-1：使用數(shù)據(jù)庫(kù)時(shí)函數(shù)和資源之間的交互包含數(shù)據(jù)庫(kù)登錄細(xì)節(jié)我們先創(chuàng)建一個(gè)文件，用來(lái)保存登錄MySQL所用到的信息。我們建議你把這些信息放在單獨(dú)的文件里然后通過(guò)include來(lái)使用這個(gè)文件。這樣一來(lái)如果你修改了數(shù)據(jù)庫(kù)的密碼。無(wú)論有多少個(gè)PHP文件訪問(wèn)數(shù)據(jù)庫(kù)，你只需要修改這一個(gè)文件。連接到數(shù)據(jù)庫(kù)我們需要做的頭一件事情是連接數(shù)據(jù)庫(kù)，并且檢查連接是否確實(shí)建立起來(lái)。通過(guò)include包含連接信息的文件，我們可以在調(diào)用mysql_connect函數(shù)的時(shí)候使用這些變量而不是將這些值寫死在代碼中。我們使用一個(gè)叫做db_test.php的文件，往其中增加這些代碼段。診斷連接錯(cuò)誤你可能遇到的一個(gè)錯(cuò)誤是：Fatal error: Call to undefined function mysql_connect( ) in C:Program FilesApacheSoftware FoundationApache2.2htdocsdb_test.php on line 4這個(gè)錯(cuò)誤發(fā)生的原因是下載安裝的PHP5.x默認(rèn)沒(méi)有包括對(duì)MySQL的支持。解決這個(gè)問(wèn)題需要將php_mysql.dll文件從PHP壓縮包例的ext/目錄復(fù)制到C:/php，并修改C:WINDOWSphp.ini文件，確保下面兩行沒(méi)有被注釋掉（注釋的方法在行首使用分號(hào)）。extension_dir = c:/PHP/ext/extension=php_mysql.dll這樣PHP擴(kuò)展的目錄就被設(shè)為C:PHP,MySQL的擴(kuò)展也會(huì)被使用。在編輯php.ini文件的時(shí)候，你可以使用編輯器的搜索功能來(lái)檢查這兩行是否已經(jīng)存在，只是需要去掉注釋，并且需要重新輸入。重新啟動(dòng)Apache，這樣MySQL的支持就會(huì)被打開了。選擇數(shù)據(jù)庫(kù)建立連接之后，下一步就是使用mysql_select_db來(lái)選擇我們要用的數(shù)據(jù)庫(kù)。它的參數(shù)有兩個(gè)：數(shù)據(jù)庫(kù)名和可選的數(shù)據(jù)庫(kù)連接。如果不指定數(shù)據(jù)庫(kù)連接，默認(rèn)使用上一條mysql_connect所建立的連接。/ Select the database$db_select=mysql_select_db($db_database);if (!$db_select)die (Could not select the database: . mysql_error( );同樣的，每次訪問(wèn)數(shù)據(jù)庫(kù)的時(shí)候最好能檢查可能的錯(cuò)誤并且進(jìn)行顯示?，F(xiàn)在我們做好了一切準(zhǔn)備工作，可以開始執(zhí)行SQL查詢了。構(gòu)建SQL SELECT查詢構(gòu)建SQL查詢非常容易就是將一個(gè)字符串賦值給變量。這個(gè)字符串就是我們的SQL查詢，當(dāng)然我們要給出有效的SQL查詢，否則執(zhí)行這個(gè)查詢的時(shí)候MySQL會(huì)返回錯(cuò)誤。我們使用$query作為變量名，這個(gè)名字對(duì)應(yīng)其目的，你也可以選擇任何你喜歡的變量名。這個(gè)例子中的SQL查詢是”SELECT * FROM books”。你可以使用字符串連接操作符（.）來(lái)構(gòu)建查詢：執(zhí)行查詢使用mysql_query函數(shù)來(lái)告訴數(shù)據(jù)庫(kù)執(zhí)行查詢。它有兩個(gè)參數(shù)：查詢和可選的數(shù)據(jù)庫(kù)連接，返回值是查詢結(jié)果。我們將查詢結(jié)果保存在一個(gè)變量里，也許你已經(jīng)猜到我們要用變量名就是$result。這里同樣有必要檢查mysql_query的返回值不是FALSE來(lái)確保查詢字符串和數(shù)據(jù)庫(kù)連接都沒(méi)有問(wèn)題。當(dāng)數(shù)據(jù)庫(kù)查詢的時(shí)候，所有的結(jié)果構(gòu)成一個(gè)結(jié)果集。這些結(jié)果跟使用mysql命令行客戶端執(zhí)行同樣查詢所得到的行一致。要顯示這些結(jié)果，你需要依次處理這些行。取結(jié)果并顯示使用mysql_fetch_row從結(jié)果集中取出一行，它的用法如下：array mysql_fetch_row ( resource $result);它的參數(shù)是SQL查詢返回的結(jié)果，我們將結(jié)果保存在$result中。每次調(diào)用它返回一行數(shù)據(jù)，直到?jīng)]有數(shù)據(jù)為止，這時(shí)候它返回FALSE。這樣，我們可以使用一個(gè)循環(huán)，在循環(huán)內(nèi)調(diào)用mysql_fetch_row并使用一些代碼來(lái)顯示每一行。結(jié)果行的所有列都保存在一個(gè)數(shù)組里，可以方便地進(jìn)行訪問(wèn)。變量$result_row2訪問(wèn)結(jié)果行的第二個(gè)屬性（數(shù)組的順序是查詢是定義的列的順序，如果使用SELECE * ，那么數(shù)組順序就是表的列的順序）。取結(jié)果的方式去結(jié)果的方式不止一種。使用mysql_fetch_arrry可以一次性將所有結(jié)果放在一個(gè)數(shù)組里。它的參數(shù)是查詢結(jié)果和一個(gè)可選的結(jié)果綁定方式。如果綁定方式指定為MYSQL_ASSOC，數(shù)組中的結(jié)果則使用查詢中列的名字進(jìn)行訪問(wèn)。如果指定了MYSQL_NUM，那么就使用從0開始的數(shù)字來(lái)訪問(wèn)結(jié)果。默認(rèn)使用的方式是MYSQL_BOTH，這樣返回的數(shù)組支持兩種類型的訪問(wèn)。Mysql_fetch_assoc是使用MYSQL_ASSOC取結(jié)果的另外一種方式。關(guān)閉連接絕大部分情況下，我們?cè)谑褂猛暌粋€(gè)數(shù)據(jù)庫(kù)之后要關(guān)閉到它的連接。使用mysql_close來(lái)關(guān)閉一個(gè)數(shù)據(jù)庫(kù)，它會(huì)告訴PHP和MySQL這個(gè)數(shù)據(jù)庫(kù)連接已經(jīng)不再使用，所使用的所有資源和內(nèi)存都可以釋放。mysql_close($connection)安裝PEAR使用包管理器來(lái)管理安裝PEAR模塊。是否需要安裝包管理取決于你所使用的PHP版本。如果你使用的版本是PHP4.4.0或者更新的版本，那么就已經(jīng)安裝了包管理器。如果你使用的是PHP5.0,則PEAR是一個(gè)單獨(dú)的包。我們要用到的DB包是可選的，但是它會(huì)被包管理器默認(rèn)安裝。所以，如果你有包管理器，那么就全搞定了。UNIX在UNIX系統(tǒng)下，