Wordpress Query Parameters Post & Page Parameter

Display post by ID:
$query = new WP_Query( array( 'p' => 7 ) );

Display page by ID:
$query = new WP_Query( array( 'page_id' => 7 ) );

Show post/page by slug
$query = new WP_Query( array( 'name' => 'about-my-life' ) );

Display page by slug:
$query = new WP_Query( array( 'pagename' => 'contact' ) );

Display child page using the slug of the parent and the child page, separated by a slash (e.g. ‘parent_slug/child_slug’):
$query = new WP_Query( array( 'pagename' => 'contact_us/canada' ) );

Display child pages using parent page ID:
$query = new WP_Query( array( 'post_parent' => 93 ) );

Display only top-level pages, exclude all child pages:
$query = new WP_Query( array( 'post_parent' => 0 ) );

Display posts whose parent is in an array:
$query = new WP_Query( array( 'post_parent__in' => array( 2, 5, 12, 14, 20 ) ) );

Display only the specific posts:
$query = new WP_Query( array( 'post_type' => 'page', 'post__in' => array( 2, 5, 12, 14, 20 ) ) );

Display all posts but NOT the specified ones:
$query = new WP_Query( array( 'post_type' => 'post', 'post__not_in' => array( 2, 5, 12, 14, 20 ) ) );