要安全高效地在WordPress中運(yùn)行自定義數(shù)據(jù)庫(kù)查詢，應(yīng)使用內(nèi)置的wpdb類(lèi)。 1. 使用全局變量$wpdb並理解其基本屬性如$wpdb->prefix；2. 運(yùn)行SELECT查詢時(shí)使用$wpdb->prepare()方法防止SQL注入，根據(jù)結(jié)果數(shù)量選擇get_results、get_row或get_var；3. 插入、更新和刪除數(shù)據(jù)時(shí)使用insert()、update()和delete()方法，並確保格式正確；4. 調(diào)試時(shí)檢查last_error和last_query以處理錯(cuò)誤；5. 注意性能與安全最佳實(shí)踐，如避免原始查詢、對(duì)輸入輸出進(jìn)行過(guò)濾和轉(zhuǎn)義、使用索引及分頁(yè)處理大數(shù)據(jù)集。

When you need to run custom database queries in WordPress, the wpdb class is your go-to tool. It's a built-in PHP class that allows you to interact directly with the WordPress database safely and efficiently. While it's powerful, using it correctly requires understanding a few key practices.

Understanding the Basics of $wpdb

The wpdb class is already instantiated as a global variable called $wpdb . You can access it by declaring global $wpdb; at the top of your function or script. This object gives you direct access to the current site's database tables.

Some basic properties you might use:

• $wpdb->prefix – the table prefix (like wp_ )
• $wpdb->base_prefix – the original prefix before any dynamic changes
• $wpdb->dbname , $wpdb->dbuser , etc. – for connection details (rarely needed)

You typically don't need to create a new instance — just use the global one.

Running SELECT Queries Safely

For retrieving data from the database, use $wpdb->get_results() or $wpdb->get_row() depending on how many results you expect.

Best practice: Always use placeholders and the $wpdb->prepare() method to avoid SQL injection:

 global $wpdb;

$user_id = 123;
$results = $wpdb->get_results( $wpdb->prepare(
    "SELECT * FROM {$wpdb->prefix}users WHERE ID = %d",
    $user_id
) );

• %d is for integers
• %s is for strings
• %f is for floats

This ensures values are properly escaped and safe to use.

If you're only expecting one row:

 $row = $wpdb->get_row( $wpdb->prepare(
    "SELECT user_login FROM {$wpdb->prefix}users WHERE ID = %d",
    $user_id
) );

And if you want a single value:

 $username = $wpdb->get_var( $wpdb->prepare(
    "SELECT user_login FROM {$wpdb->prefix}users WHERE ID = %d",
    $user_id
) );

Inserting, Updating, and Deleting Data

For modifying data, $wpdb provides helper methods like insert() , update() , and delete() .

These methods accept table names, data arrays, and where clauses, and they return the number of affected rows or false on failure.

Example of inserting a row:

 global $wpdb;

$data = array(
    'name' => 'John Doe',
    'email' => 'john@example.com'
);

$format = array(
    '%s', // name is a string
    '%s' // email is a string
);

$wpdb->insert( 'my_custom_table', $data, $format );

Updating a record:

 $wpdb->update(
    'my_custom_table',
    array( 'email' => 'new_email@example.com' ),
    array( 'id' => 123 ), // where clause
    array( '%s' ),
    array( '%d' )
);

Deleting records:

 $wpdb->delete(
    'my_custom_table',
    array( 'id' => 123 ),
    array( '%d' )
);

Using these methods helps keep your code clean and reduces chances of errors.

Debugging and Error Handling

By default, WordPress doesn't show database errors unless you enable debugging.

To check for errors during query execution, use $wpdb->last_error after running a query:

 $results = $wpdb->get_results("SELECT * FROM non_existing_table");
if ( ! $results ) {
    echo 'Database error: ' . $wpdb->last_error;
}

Also useful:

• $wpdb->last_query – shows the last executed query
• $wpdb->print_error() – outputs the last error message (not recommended in production)

In development, consider setting define('WP_DEBUG', true); in wp-config.php to catch more issues early.

Final Notes on Performance and Security

A few things to keep in mind when working with $wpdb :

• Avoid raw queries when built-in functions exist (eg, get_post_meta() instead of querying postmeta directly)
• Always sanitize input and escape output
• Use indexes in custom tables for faster lookups
• Be cautious with large datasets – pagination ( LIMIT , OFFSET ) helps prevent timeouts

Using $wpdb effectively comes down to knowing when to use it and how to protect yourself from common pitfalls. Keep your queries simple, secure, and well-structured, and you'll be fine.

基本上就這些。

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