global $wpdb;
$results = $wpdb->get_results( "SELECT * FROM {$wpdb->posts}" );

public function __construct( $dbuser, $dbpassword, $dbname, $dbhost )

public function query( $query ): int|bool

// SELECT - returns row count
$count = $wpdb->query( "SELECT * FROM {$wpdb->posts}" );

// UPDATE - returns affected rows
$affected = $wpdb->query( 
    $wpdb->prepare( "UPDATE {$wpdb->posts} SET post_status = %s WHERE ID = %d", 'draft', 123 )
);

// CREATE - returns true
$result = $wpdb->query( "CREATE TABLE my_table (id INT)" );

public function get_var( $query = null, $x = 0, $y = 0 ): string|null

// Count posts
$count = $wpdb->get_var( "SELECT COUNT(*) FROM {$wpdb->posts}" );

// Get specific value
$title = $wpdb->get_var( 
    $wpdb->prepare( "SELECT post_title FROM {$wpdb->posts} WHERE ID = %d", 123 )
);

// Get from cached result (different column)
$wpdb->query( "SELECT post_title, post_date FROM {$wpdb->posts} LIMIT 1" );
$title = $wpdb->get_var( null, 0 ); // First column
$date = $wpdb->get_var( null, 1 );  // Second column

public function get_row( $query = null, $output = OBJECT, $y = 0 ): array|object|null|void

// As object
$row = $wpdb->get_row( 
    $wpdb->prepare( "SELECT * FROM {$wpdb->posts} WHERE ID = %d", 123 )
);
echo $row->post_title;

// As associative array
$row = $wpdb->get_row( 
    $wpdb->prepare( "SELECT * FROM {$wpdb->posts} WHERE ID = %d", 123 ),
    ARRAY_A
);
echo $row['post_title'];

// As numeric array
$row = $wpdb->get_row( 
    $wpdb->prepare( "SELECT * FROM {$wpdb->posts} WHERE ID = %d", 123 ),
    ARRAY_N
);
echo $row[0]; // First column

public function get_col( $query = null, $x = 0 ): array

// Get all post IDs
$ids = $wpdb->get_col( "SELECT ID FROM {$wpdb->posts} WHERE post_status = 'publish'" );
// Returns: array( 1, 2, 3, 4, ... )

// Get second column from cached result
$wpdb->query( "SELECT ID, post_title FROM {$wpdb->posts}" );
$titles = $wpdb->get_col( null, 1 );

public function get_results( $query = null, $output = OBJECT ): array|object|null

// Array of objects
$posts = $wpdb->get_results( "SELECT * FROM {$wpdb->posts} LIMIT 10" );
foreach ( $posts as $post ) {
    echo $post->post_title;
}

// Keyed by ID
$posts = $wpdb->get_results( 
    "SELECT ID, post_title FROM {$wpdb->posts}", 
    OBJECT_K 
);
echo $posts[123]->post_title; // Access by ID

// Array of associative arrays
$posts = $wpdb->get_results( 
    "SELECT * FROM {$wpdb->posts}", 
    ARRAY_A 
);
foreach ( $posts as $post ) {
    echo $post['post_title'];
}

public function insert( $table, $data, $format = null ): int|false

// Basic insert
$wpdb->insert(
    $wpdb->postmeta,
    array(
        'post_id'    => 123,
        'meta_key'   => '_custom_key',
        'meta_value' => 'custom_value',
    )
);
$meta_id = $wpdb->insert_id;

// With explicit formats
$wpdb->insert(
    $wpdb->posts,
    array(
        'post_title'   => 'Hello World',
        'post_content' => 'Content here',
        'post_status'  => 'publish',
        'post_author'  => 1,
    ),
    array( '%s', '%s', '%s', '%d' )
);

// NULL values
$wpdb->insert(
    $wpdb->posts,
    array(
        'post_title'  => 'Title',
        'post_parent' => null, // Sets to NULL
    )
);

public function replace( $table, $data, $format = null ): int|false

// Replace existing or insert new
$wpdb->replace(
    $wpdb->options,
    array(
        'option_name'  => 'my_option',
        'option_value' => 'new_value',
        'autoload'     => 'yes',
    ),
    array( '%s', '%s', '%s' )
);

public function update( $table, $data, $where, $format = null, $where_format = null ): int|false

// Update post
$wpdb->update(
    $wpdb->posts,
    array(
        'post_title'  => 'New Title',
        'post_status' => 'draft',
    ),
    array( 'ID' => 123 ),
    array( '%s', '%s' ),
    array( '%d' )
);

// Update with NULL in WHERE
$wpdb->update(
    $wpdb->posts,
    array( 'post_status' => 'trash' ),
    array( 'post_parent' => null ) // WHERE post_parent IS NULL
);

public function delete( $table, $where, $where_format = null ): int|false

// Delete post meta
$wpdb->delete(
    $wpdb->postmeta,
    array(
        'post_id'  => 123,
        'meta_key' => '_custom_key',
    ),
    array( '%d', '%s' )
);

// Delete by NULL
$wpdb->delete(
    $wpdb->posts,
    array( 'post_author' => null ) // WHERE post_author IS NULL
);

public function prepare( $query, ...$args ): string|void

// Basic usage
$sql = $wpdb->prepare(
    "SELECT * FROM {$wpdb->posts} WHERE ID = %d AND post_status = %s",
    123,
    'publish'
);

// Array of arguments
$sql = $wpdb->prepare(
    "SELECT * FROM {$wpdb->posts} WHERE ID = %d",
    array( 123 )
);

// Identifier placeholder
$sql = $wpdb->prepare(
    "SELECT * FROM %i WHERE %i = %s",
    'my_table',
    'my_column',
    'value'
);

// Numbered placeholders
$sql = $wpdb->prepare(
    "SELECT * FROM {$wpdb->posts} WHERE post_author = %1$d OR post_parent = %1$d",
    $user_id
);

// Escaping literal %
$sql = $wpdb->prepare(
    "SELECT DATE_FORMAT(post_date, '%%Y-%%m-%%d') FROM {$wpdb->posts} WHERE ID = %d",
    123
);

public function esc_like( $text ): string

$search = '%test_value%';
$like = '%' . $wpdb->esc_like( $search ) . '%';
$sql = $wpdb->prepare(
    "SELECT * FROM {$wpdb->posts} WHERE post_title LIKE %s",
    $like
);
// Result: WHERE post_title LIKE '%%test_value%%'

public function _real_escape( $data ): string

public function _escape( $data ): string|array

public function escape_by_ref( &$data ): void

public function quote_identifier( $identifier ): string

$quoted = $wpdb->quote_identifier( 'table_name' );
// Returns: `table_name`

$quoted = $wpdb->quote_identifier( 'col`name' );
// Returns: `col``name` (backtick escaped)

public function tables( $scope = 'all', $prefix = true, $blog_id = 0 ): string[]

// All tables with prefix
$tables = $wpdb->tables();
// array( 'posts' => 'wp_posts', 'comments' => 'wp_comments', ... )

// Blog-specific tables only
$tables = $wpdb->tables( 'blog' );

// Global tables only
$tables = $wpdb->tables( 'global' );

// Without prefixes
$tables = $wpdb->tables( 'all', false );
// array( 'posts', 'comments', 'users', ... )

public function set_prefix( $prefix, $set_table_names = true ): string|WP_Error

public function get_blog_prefix( $blog_id = null ): string

$prefix = $wpdb->get_blog_prefix( 2 );
// Returns: wp_2_ (for blog ID 2 in multisite)

public function set_blog_id( $blog_id, $network_id = 0 ): int

public function db_connect( $allow_bail = true ): bool

public function check_connection( $allow_bail = true ): bool|void

public function select( $db, $dbh = null ): void

public function close(): bool

public function parse_db_host( $host ): array|false

public function show_errors( $show = true ): bool

public function hide_errors(): bool

public function suppress_errors( $suppress = true ): bool

public function print_error( $str = '' ): void|false

public function bail( $message, $error_code = '500' ): void|false

public function init_charset(): void

public function determine_charset( $charset, $collate ): array

public function set_charset( $dbh, $charset = null, $collate = null ): void

public function get_charset_collate(): string

$charset_collate = $wpdb->get_charset_collate();
$sql = "CREATE TABLE my_table (
    id INT AUTO_INCREMENT,
    name VARCHAR(255),
    PRIMARY KEY (id)
) $charset_collate";

protected function get_table_charset( $table ): string|WP_Error

public function get_col_charset( $table, $column ): string|false|WP_Error

public function get_col_length( $table, $column ): array|false|WP_Error

public function set_sql_mode( $modes = array() ): void

public function has_cap( $db_cap ): bool

if ( $wpdb->has_cap( 'utf8mb4_520' ) ) {
    // Use better collation
}

public function get_col_info( $info_type = 'name', $col_offset = -1 ): mixed

$wpdb->query( "SELECT * FROM {$wpdb->posts} LIMIT 1" );

// Get all column names
$names = $wpdb->get_col_info( 'name' );

// Get specific column's max length
$max_length = $wpdb->get_col_info( 'max_length', 0 );

public function flush(): void

public function db_version(): string|null

public function db_server_info(): string

public function check_database_version(): void|WP_Error

public function timer_start(): true

public function timer_stop(): float

public function get_caller(): string

public function log_query( $query, $query_time, $query_callstack, $query_start, $query_data ): void

public function strip_invalid_text_for_column( $table, $column, $value ): string|WP_Error

protected function check_ascii( $input_string ): bool

public function placeholder_escape(): string

public function add_placeholder_escape( $query ): string

public function remove_placeholder_escape( $query ): string

public function __get( $name ): mixed

public function __set( $name, $value ): void

public function __isset( $name ): bool

public function __unset( $name ): void

public function supports_collation(): bool

public function escape( $data ): string|array

public function _weak_escape( $data ): string