小新 
匿名 mysql基础
PHP 5 及以上版本建议使用以下方式连接 MySQL :
- MySQLi extension ("i" 意为 improved)
- PDO (PHP Data Objects)
我是该用 MySQLi ，还是 PDO?
如果你需要一个简短的回答，即 "你习惯哪个就用哪个"。
MySQLi 和 PDO 有它们自己的优势：
PDO 应用在 12 种不同数据库中， MySQLi 只针对 MySQL 数据库。
所以，如果你的项目需要在多种数据库中切换，建议使用 PDO ，这样你只需要修改连接字符串和部分查询语句即可。 使用 MySQLi, 如果不同数据库，你需要重新编写所有代码，包括查询。
两者都是面向对象, 但 MySQLi 还提供了 API 接口。
两者都支持预处理语句。 预处理语句可以防止 SQL 注入，对于 web 项目的安全性是非常重要的。
连接 MySQL
实例 (MySQLi - 面向对象)
♾️ php 代码:<?php
$servername = "localhost";
$username = "username";
$password = "password";
// 创建连接
$conn = new mysqli($servername, $username, $password);
// 检测连接
if ($conn->connect_error) {
die("连接失败: " . $conn->connect_error);
}
echo "连接成功";
?>实例 (MySQLi - 面向过程)
♾️ php 代码:<?php
$servername = "localhost";
$username = "username";
$password = "password";
// 创建连接
$conn = mysqli_connect($servername, $username, $password);
// 检测连接
if (!$conn) {
die("Connection failed: " . mysqli_connect_error());
}
echo "连接成功";
?>实例 (PDO)
♾️ php 代码:<?php
$servername = "localhost";
$username = "username";
$password = "password";
try {
$conn = new PDO("mysql:host=$servername;", $username, $password);
echo "连接成功";
}
catch(PDOException $e)
{
echo $e->getMessage();
}
?>关闭连接
实例 (MySQLi - 面向对象)
♾️ php 代码:$conn->close();实例 (MySQLi - 面向过程)
♾️ php 代码:mysqli_close($conn);实例 (PDO)
♾️ php 代码:$conn = null;对数据库进行操作
实例 (MySQLi - 面向对象)
♾️ php 代码:<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";
// 创建连接
$conn = new mysqli($servername, $username, $password, $dbname);
// 检测连接
if ($conn->connect_error) {
die("连接失败: " . $conn->connect_error);
}
$sql = "INSERT INTO MyGuests (firstname, lastname, email)
VALUES ('John', 'Doe', 'john@example.com')";
if ($conn->query($sql) === TRUE) {
echo "新记录插入成功";
} else {
echo "Error: " . $sql . "<br>" . $conn->error;
}
$conn->close();
?>实例 (MySQLi - 面向过程)
♾️ php 代码:<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";
// 创建连接
$conn = mysqli_connect($servername, $username, $password, $dbname);
// 检测连接
if (!$conn) {
die("Connection failed: " . mysqli_connect_error());
}
$sql = "INSERT INTO MyGuests (firstname, lastname, email)
VALUES ('John', 'Doe', 'john@example.com')";
if (mysqli_query($conn, $sql)) {
echo "新记录插入成功";
} else {
echo "Error: " . $sql . "<br>" . mysqli_error($conn);
}
mysqli_close($conn);
?>实例 (PDO)
♾️ php 代码:<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDBPDO";
try {
$conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
// 设置 PDO 错误模式，用于抛出异常
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$sql = "INSERT INTO MyGuests (firstname, lastname, email)
VALUES ('John', 'Doe', 'john@example.com')";
// 使用 exec() ，没有结果返回
$conn->exec($sql);
echo "新记录插入成功";
}
catch(PDOException $e)
{
echo $sql . "<br>" . $e->getMessage();
}
$conn = null;
?>执行多条sql语句
实例 (MySQLi - 面向对象)
♾️ php 代码:<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";
// 创建链接
$conn = new mysqli($servername, $username, $password, $dbname);
// 检查链接
if ($conn->connect_error) {
die("连接失败: " . $conn->connect_error);
}
$sql = "INSERT INTO MyGuests (firstname, lastname, email)
VALUES ('John', 'Doe', 'john@example.com');";
$sql .= "INSERT INTO MyGuests (firstname, lastname, email)
VALUES ('Mary', 'Moe', 'mary@example.com');";
$sql .= "INSERT INTO MyGuests (firstname, lastname, email)
VALUES ('Julie', 'Dooley', 'julie@example.com')";
if ($conn->multi_query($sql) === TRUE) {
echo "新记录插入成功";
} else {
echo "Error: " . $sql . "<br>" . $conn->error;
}
$conn->close();
?>实例 (MySQLi - 面向过程)
♾️ php 代码:<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";
// 创建链接
$conn = mysqli_connect($servername, $username, $password, $dbname);
// 检查链接
if (!$conn) {
die("连接失败: " . mysqli_connect_error());
}
$sql = "INSERT INTO MyGuests (firstname, lastname, email)
VALUES ('John', 'Doe', 'john@example.com');";
$sql .= "INSERT INTO MyGuests (firstname, lastname, email)
VALUES ('Mary', 'Moe', 'mary@example.com');";
$sql .= "INSERT INTO MyGuests (firstname, lastname, email)
VALUES ('Julie', 'Dooley', 'julie@example.com')";
if (mysqli_multi_query($conn, $sql)) {
echo "新记录插入成功";
} else {
echo "Error: " . $sql . "<br>" . mysqli_error($conn);
}
mysqli_close($conn);
?>实例 (PDO) 事务操作
♾️ php 代码:<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDBPDO";
try {
$conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
// set the PDO error mode to exception
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
// 开始事务
$conn->beginTransaction();
// SQL 语句
$conn->exec("INSERT INTO MyGuests (firstname, lastname, email)
VALUES ('John', 'Doe', 'john@example.com')");
$conn->exec("INSERT INTO MyGuests (firstname, lastname, email)
VALUES ('Mary', 'Moe', 'mary@example.com')");
$conn->exec("INSERT INTO MyGuests (firstname, lastname, email)
VALUES ('Julie', 'Dooley', 'julie@example.com')");
// 提交事务
$conn->commit();
echo "新记录插入成功";
}
catch(PDOException $e)
{
// 如果执行失败回滚
$conn->rollback();
echo $sql . "<br>" . $e->getMessage();
}
$conn = null;
?>数据查询
实例 (MySQLi - 面向对象)
♾️ php 代码:<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";
// 创建连接
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
die("连接失败: " . $conn->connect_error);
}
$sql = "SELECT id, firstname, lastname FROM MyGuests";
$result = $conn->query($sql);
if ($result->num_rows > 0) {
// 输出数据
while($row = $result->fetch_assoc()) {
echo "id: " . $row["id"]. " - Name: " . $row["firstname"]. " " . $row["lastname"]. "<br>";
}
} else {
echo "0 结果";
}
$conn->close();
?>实例 (MySQLi - 面向过程)
♾️ php 代码:<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";
// 创建连接
$conn = mysqli_connect($servername, $username, $password, $dbname);
// Check connection
if (!$conn) {
die("连接失败: " . mysqli_connect_error());
}
$sql = "SELECT id, firstname, lastname FROM MyGuests";
$result = mysqli_query($conn, $sql);
if (mysqli_num_rows($result) > 0) {
// 输出数据
while($row = mysqli_fetch_assoc($result)) {
echo "id: " . $row["id"]. " - Name: " . $row["firstname"]. " " . $row["lastname"]. "<br>";
}
} else {
echo "0 结果";
}
mysqli_close($conn);
?>使用 PDO (+ 预处理)
♾️ php 代码:<?php
echo "<table style='border: solid 1px black;'>";
echo "<tr><th>Id</th><th>Firstname</th><th>Lastname</th></tr>";
class TableRows extends RecursiveIteratorIterator {
function __construct($it) {
parent::__construct($it, self::LEAVES_ONLY);
}
function current() {
return "<td style='width:150px;border:1px solid black;'>" . parent::current(). "</td>";
}
function beginChildren() {
echo "<tr>";
}
function endChildren() {
echo "</tr>" . "\n";
}
}
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDBPDO";
try {
$conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$stmt = $conn->prepare("SELECT id, firstname, lastname FROM MyGuests");
$stmt->execute();
// 设置结果集为关联数组
$result = $stmt->setFetchMode(PDO::FETCH_ASSOC);
foreach(new TableRows(new RecursiveArrayIterator($stmt->fetchAll())) as $k=>$v) {
echo $v;
}
}
catch(PDOException $e) {
echo "Error: " . $e->getMessage();
}
$conn = null;
echo "</table>";
?>遇到错误
在学习 PDO 创建数据表的时候 ， 我遇到这个报错。♾️ php 代码:
SQLSTATE[3D000]: Invalid catalog name: 1046 No database selected最后发现问题在这里：♾️ php 代码:
$conn = new PDO("mysql:host = $servername;dbname = $dbname",$username,$password);因为我写代码的习惯是" = "两边都加上空格 ， 但是在这里 dbname = $dbname 的等号两边却不可以存在空格所以正确的写法应该是 dbname=$dbname：♾️ php 代码:
$conn = new PDO("mysql:host = $servername;dbname=$dbname",$username,$password);