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Translating by MjSeven
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The Easiest PDO Tutorial (Basics)
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======
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Approximately 80% of the web is powered by PHP. And similarly, high number goes for SQL as well. Up until PHP version 5.5, we had the **mysql_** commands for accessing mysql databases but they were eventually deprecated due to insufficient security.
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This happened with PHP 5.5 in 2013 and as I write this article, the year is 2018 and we are on PHP 7.2. The deprecation of mysql**_** brought 2 major ways of accessing the database, the **mysqli** and the **PDO** libraries.
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Now though the mysqli library was the official successor, PDO gained more fame due to a simple reason that mysqli could only support mysql databases whereas PDO could support 12 different types of database drivers. Also, PDO had several more features that made it the better choice for most developers. You can see some of the feature comparisons in the table below;
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| | PDO | MySQLi |
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| Database support** | 12 drivers | Only MySQL |
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| Paradigm | OOP | Procedural + OOP |
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| Prepared Statements Client Side) | Yes | No |
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| Named Parameters | Yes | No |
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Now I guess it is pretty clear why PDO is the choice for most developers, so let’s dig into it and hopefully we will try to cover most of the PDO you need in this article itself.
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### Connection
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The first step is connecting to the database and since PDO is completely Object Oriented, we will be using the instance of a PDO class.
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The first thing we do is we define the host, database name, user, password and the database charset.
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`$host = 'localhost';`
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`$db = 'theitstuff';`
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`$user = 'root';`
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`$pass = 'root';`
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`$charset = 'utf8mb4';`
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`$dsn = "mysql:host=$host;dbname=$db;charset=$charset";`
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`$conn = new PDO($dsn, $user, $pass);`
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After that, as you can see in the code above we have created the **DSN** variable, the DSN variable is simply a variable that holds the information about the database. For some people running mysql on external servers, you could also adjust your port number by simply supplying a **port=$port_number**.
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Finally, you can create an instance of the PDO class, I have used the **$conn** variable and I have supplied the **$dsn, $user, $pass** parameters. If you have followed this, you should now have an object named $conn that is an instance of the PDO connection class. Now it’s time to get into the database and run some queries.
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### A simple SQL Query
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Let us now run a simple SQL query.
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`$tis = $conn->query('SELECT name, age FROM students');`
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`while ($row = $tis->fetch())`
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`{`
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`echo $row['name']."\t";`
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`echo $row['age'];`
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`echo "<br>";`
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`}`
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This is the simplest form of running a query with PDO. We first created a variable called **tis( **short for TheITStuff** )** and then you can see the syntax as we used the query function from the $conn object that we had created.
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We then ran a while loop and created a **$row** variable to fetch the contents from the **$tis** object and finally echoed out each row by calling out the column name.
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Easy wasn’t it ?. Now let’s get to the prepared statement.
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### Prepared Statements
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Prepared statements were one of the major reasons people started using PDO as it had prepared statements that could prevent SQL injections.
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There are 2 basic methods available, you could either use positional or named parameters.
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#### Position parameters
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Let us see an example of a query using positional parameters.
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`$tis = $conn->prepare("INSERT INTO STUDENTS(name, age) values(?, ?)");`
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`$tis->bindValue(1,'mike');`
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`$tis->bindValue(2,22);`
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`$tis->execute();`
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In the above example, we have placed 2 question marks and later used the **bindValue()** function to map the values into the query. The values are bound to the position of the question mark in the statement.
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I could also use variables instead of directly supplying values by using the **bindParam()** function and example for the same would be this.
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`$name='Rishabh'; $age=20;`
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`$tis = $conn->prepare("INSERT INTO STUDENTS(name, age) values(?, ?)");`
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`$tis->bindParam(1,$name);`
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`$tis->bindParam(2,$age);`
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`$tis->execute();`
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### Named Parameters
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Named parameters are also prepared statements that map values/variables to a named position in the query. Since there is no positional binding, it is very efficient in queries that use the same variable multiple time.
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`$name='Rishabh'; $age=20;`
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`$tis = $conn->prepare("INSERT INTO STUDENTS(name, age) values(:name, :age)");`
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`$tis->bindParam(':name', $name);`
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`$tis->bindParam(':age', $age);`
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`$tis->execute();`
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The only change you can notice is that I used **:name** and **:age** as placeholders and then mapped variables to them. The colon is used before the parameter and it is of extreme importance to let PDO know that the position is for a variable.
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You can similarly use **bindValue()** to directly map values using Named parameters as well.
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### Fetching the Data
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PDO is very rich when it comes to fetching data and it actually offers a number of formats in which you can get the data from your database.
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You can use the **PDO::FETCH_ASSOC** to fetch associative arrays, **PDO::FETCH_NUM** to fetch numeric arrays and **PDO::FETCH_OBJ** to fetch object arrays.
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`$tis = $conn->prepare("SELECT * FROM STUDENTS");`
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`$tis->execute();`
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`$result = $tis->fetchAll(PDO::FETCH_ASSOC);`
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You can see that I have used **fetchAll** since I wanted all matching records. If only one row is expected or desired, you can simply use **fetch.**
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Now that we have fetched the data it is time to loop through it and that is extremely easy.
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`foreach($result as $lnu){`
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`echo $lnu['name'];`
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`echo $lnu['age']."<br>";`
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`}`
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You can see that since I had requested associative arrays, I am accessing individual members by their names.
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Though there is absolutely no problem in defining how you want your data delivered, you could actually set one as default when defining the connection variable itself.
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All you need to do is create an options array where you put in all your default configs and simply pass the array in the connection variable.
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`$options = [`
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` PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,`
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`];`
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`$conn = new PDO($dsn, $user, $pass, $options);`
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This was a very brief and quick intro to PDO we will be making an advanced tutorial soon. If you had any difficulties understanding any part of the tutorial, do let me know in the comment section and I’ll be there for you.
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--------------------------------------------------------------------------------
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via: http://www.theitstuff.com/easiest-pdo-tutorial-basics
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作者：[Rishabh Kandari][a]
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选题：[lujun9972](https://github.com/lujun9972)
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]:http://www.theitstuff.com/author/reevkandari
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最简单的 PDO 教程（基础知识）
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======
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大约 80% 的 Web 应用程序由 PHP 提供支持。类似地，SQL 也是如此。PHP 5.5 版本之前，我们有用于访问 mysql 数据库的 **mysql_** 命令，但由于安全性不足，它们最终被弃用。
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**这发生在 2013 年的 PHP 5.5 上，我写这篇文章的时间是 2018 年，PHP 版本为 7.2。mysql_** 的弃用带来了访问数据库的两种主要方法：**mysqli** 和 **PDO** 库。
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虽然 mysqli 库是官方指定的，但由于 mysqli 只能支持 mysql 数据库，而 PDO 可以支持 12 种不同类型的数据库驱动程序，因此 PDO 获得了更多的赞誉。此外，PDO 还有其它一些特性，使其成为大多数开发人员的更好选择。你可以在下表中看到一些特性比较：
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| | PDO | MySQLi
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---|---|---
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| **数据库支持** | 12 种驱动 | 只有 MySQL
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| **范例** | OOP | 过程 + OOP
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| **预处理语句（客户端侧）** | Yes | No
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| **命名参数** | Yes | No
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现在我想对于大多数开发人员来说，PDO 是首选的原因已经很清楚了。所以让我们深入研究它，并希望在本文中尽量涵盖关于 PDO 你需要的了解的。
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### 连接
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第一步是连接到数据库，由于 PDO 是完全面向对象的，所以我们将使用 PDO 类的实例。
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我们要做的第一件事是定义主机、数据库名称、用户名、密码和数据库字符集。
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`$host = 'localhost';`
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`$db = 'theitstuff';`
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`$user = 'root';`
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`$pass = 'root';`
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`$charset = 'utf8mb4';`
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`$dsn = "mysql:host=$host;dbname=$db;charset=$charset";`
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`$conn = new PDO($dsn, $user, $pass);`
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之后，正如你在上面的代码中看到的，我们创建了 **DSN** 变量，DSN 变量只是一个保存数据库信息的变量。对于一些在外部服务器上运行 mysql 的人，你还可以通过提供一个 **port=$port_number** 来调整端口号。
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最后，你可以创建一个 PDO 类的实例，我使用了 **\$conn** 变量，并提供了 **\$dsn、\$user、\$pass** 参数。如果你遵循这些步骤，你现在应该有一个名为 $conn 的对象，它是 PDO 连接类的一个实例。现在是时候进入数据库并运行一些查询。
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### 一个简单的 SQL 查询
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现在让我们运行一个简单的 SQL 查询。
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`$tis = $conn->query('SELECT name, age FROM students');`
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`while ($row = $tis->fetch())`
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`{`
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`echo $row['name']."\t";`
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`echo $row['age'];`
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`echo "<br>";`
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`}`
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这是使用 PDO 运行查询的最简单形式。我们首先创建了一个名为 **tis（TheITStuff 的缩写 ）** 的变量，然后你可以看到我们使用了创建的 $conn 对象中的查询函数。
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然后我们运行一个 while 循环并创建了一个 **$row** 变量来从 **$tis** 对象中获取内容，最后通过调用列名来显示每一行。
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很简单，不是吗？现在让我们来看看预处理语句。
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### 预处理语句
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预处理语句是人们开始使用 PDO 的主要原因之一，因为它准备了可以阻止 SQL 注入的语句。
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有两种基本方法可供使用，你可以使用位置参数或命名参数。
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#### 位置参数
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让我们看一个使用位置参数的查询示例。
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`$tis = $conn->prepare("INSERT INTO STUDENTS(name, age) values(?, ?)");`
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`$tis->bindValue(1,'mike');`
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`$tis->bindValue(2,22);`
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`$tis->execute();`
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在上面的例子中，我们放置了两个问号，然后使用 **bindValue()** 函数将值映射到查询中。这些值绑定到语句问号中的位置。
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我还可以使用变量而不是直接提供值，通过使用 **bindParam()** 函数相同例子如下：
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`$name='Rishabh'; $age=20;`
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`$tis = $conn->prepare("INSERT INTO STUDENTS(name, age) values(?, ?)");`
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`$tis->bindParam(1,$name);`
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`$tis->bindParam(2,$age);`
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`$tis->execute();`
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### 命名参数
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命名参数也是预处理语句，它将值/变量映射到查询中的命名位置。由于没有位置绑定，因此在多次使用相同变量的查询中非常有效。
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`$name='Rishabh'; $age=20;`
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`$tis = $conn->prepare("INSERT INTO STUDENTS(name, age) values(:name, :age)");`
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`$tis->bindParam(':name', $name);`
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`$tis->bindParam(':age', $age);`
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`$tis->execute();`
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你可以注意到，唯一的变化是我使用 **:name** 和 **:age** 作为占位符，然后将变量映射到它们。冒号在参数之前使用，让 PDO 知道该位置是一个变量，这非常重要。
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你也可以类似地使用 **bindValue()** 来使用命名参数直接映射值。
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### 获取数据
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PDO 在获取数据时非常丰富，它实际上提供了许多格式来从数据库中获取数据。
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你可以使用 **PDO::FETCH_ASSOC** 来获取关联数组，**PDO::FETCH_NUM** 来获取数字数组，使用 **PDO::FETCH_OBJ** 来获取对象数组。
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`$tis = $conn->prepare("SELECT * FROM STUDENTS");`
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`$tis->execute();`
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`$result = $tis->fetchAll(PDO::FETCH_ASSOC);`
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你可以看到我使用了 **fetchAll**，因为我想要所有匹配的记录。如果只需要一行，你可以简单地使用 **fetch**。
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现在我们已经获取了数据，现在是时候循环它了，这非常简单。
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`foreach($result as $lnu){`
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`echo $lnu['name'];`
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`echo $lnu['age']."<br>";`
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`}`
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你可以看到，因为我请求了关联数组，所以我正在按名称访问各个成员。
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虽然在定义希望如何传输递数据方面没有要求，但在定义 conn 变量本身时，实际上可以将其设置为默认值。
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你需要做的就是创建一个 options 数组，你可以在其中放入所有默认配置，只需在 conn 变量中传递数组即可。
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`$options = [`
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` PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,`
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`];`
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`$conn = new PDO($dsn, $user, $pass, $options);`
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这是一个非常简短和快速的 PDO 介绍，我们很快就会制作一个高级教程。如果你在理解本教程的任何部分时遇到任何困难，请在评论部分告诉我，我会在那你为你解答。
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--------------------------------------------------------------------------------
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via: http://www.theitstuff.com/easiest-pdo-tutorial-basics
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作者：[Rishabh Kandari][a]
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选题：[lujun9972](https://github.com/lujun9972)
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译者：[MjSeven](https://github.com/MjSeven)
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校对：[校对者ID](https://github.com/校对者ID)
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||||
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||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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||||
[a]:http://www.theitstuff.com/author/reevkandari
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