PHP預(yù)處理語(yǔ)句通過(guò)將SQL邏輯與數(shù)據(jù)分離來(lái)安全執(zhí)行查詢。 1. 使用佔(zhàn)位符（如?或:name）代替直接嵌入用戶輸入；2. 綁定值後再執(zhí)行，確保輸入被正確轉(zhuǎn)義，防止SQL注入；3. 提升多次執(zhí)行相似查詢時(shí)的性能；4. 使代碼更清晰易維護(hù)；5. 常見(jiàn)錯(cuò)誤包括將用戶輸入直接拼接到SQL中、忽略錯(cuò)誤處理及用佔(zhàn)位符替代表名或列名。

PHP prepared statements are a way to safely execute SQL queries by separating SQL logic from the data being passed into it. This helps prevent SQL injection attacks and makes your database interactions more efficient, especially when running similar queries multiple times with different values.

What Exactly Is a Prepared Statement?

A prepared statement is like a template for an SQL query that you define once and then fill in with actual values later. Instead of directly embedding user input into a query string, you use placeholders (like ? or :name ) and bind values to them before execution.

For example, instead of writing:

 $sql = "SELECT * FROM users WHERE id = " . $_GET['id'];

You'd do something like:

 $stmt = $pdo->prepare("SELECT * FROM users WHERE id = ?");
$stmt->execute([$_GET['id']]);

This ensures that the value is properly escaped and treated as data, not part of the SQL command.

Why You Should Use Them

There are a few solid reasons why prepared statements are the go-to method for handling dynamic SQL in PHP:

• Security First : They automatically handle escaping input, which is the main defense against SQL injection.
• Performance Boost : If you reuse the same prepared statement multiple times with different values, it's faster than parsing and compiling the whole query each time.
• Cleaner Code : Separating SQL structure from data just makes things easier to read and maintain.

Even if you're building a small app or prototype, using prepared statements is a good habit to form early.

How to Use Prepared Statements in PHP

There are two common ways to use prepared statements in PHP: using named placeholders or positional placeholders.

With Named Placeholders:

 $stmt = $pdo->prepare('INSERT INTO users (name, email) VALUES (:name, :email)');
$stmt->execute(['name' => 'John', 'email' => 'john@example.com']);

With Positional Placeholders:

 $stmt = $pdo->prepare('INSERT INTO users (name, email) VALUES (?, ?)');
$stmt->execute(['John', 'john@example.com']);

Both approaches work well. Named placeholders can be easier to manage when there are lots of values, since you can clearly see what each one represents.

Also, after executing a SELECT query, you can fetch results just like normal:

 $stmt = $pdo->prepare("SELECT name FROM users WHERE id = ?");
$stmt->execute([1]);
$user = $stmt->fetch();

Common Mistakes to Avoid

It's easy to fall into a few traps when first working with prepared statements.

• ? Don't mix raw user input directly into your SQL string even if you're using prepare/execute — the safety only comes when you bind values through execute.
• ? Don't forget to check for errors — especially in production code, always handle possible failures gracefully.
• ? Always use parameter binding for dynamic values — this includes numbers, strings, everything.

One thing people sometimes overlook is that placeholders can't be used for table names or column names. Those have to be hardcoded or carefully whitelisted in your code.

基本上就這些。

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