@type array        $include_unapproved        Array of IDs or email addresses of users whose unapproved
	 *                                                   comments will be returned by the query regardless of
	 *                                                   `$status`. Default empty.
	 *     @type int          $karma                     Karma score to retrieve matching comments for.
	 *                                                   Default empty.
	 *     @type string       $meta_key                  Include comments with a matching comment meta key.
	 *                                                   Default empty.
	 *     @type string       $meta_value                Include comments with a matching comment meta value.
	 *                                                   Requires `$meta_key` to be set. Default empty.
	 *     @type array        $meta_query                Meta query clauses to limit retrieved comments by.
	 *                                                   See WP_Meta_Query. Default empty.
	 *     @type int          $number                    Maximum number of comments to retrieve.
	 *                                                   Default empty (no limit).
	 *     @type int          $paged                     When used with $number, defines the page of results to return.
	 *                                                   When used with $offset, $offset takes precedence. Default 1.
	 *     @type int          $offset                    Number of comments to offset the query. Used to build
	 *                                                   LIMIT clause. Default 0.
	 *     @type bool         $no_found_rows             Whether to disable the `SQL_CALC_FOUND_ROWS` query.
	 *                                                   Default: true.
	 *     @type string|array $orderby                   Comment status or array of statuses. To use 'meta_value'
	 *                                                   or 'meta_value_num', `$meta_key` must also be defined.
	 *                                                   To sort by a specific `$meta_query` clause, use that
	 *                                                   clause's array key. Accepts 'comment_agent',
	 *                                                   'comment_approved', 'comment_author',
	 *                                                   'comment_author_email', 'comment_author_IP',
	 *                                                   'comment_author_url', 'comment_content', 'comment_date',
	 *                                                   'comment_date_gmt', 'comment_ID', 'comment_karma',
	 *                                                   'comment_parent', 'comment_post_ID', 'comment_type',
	 *                                                   'user_id', 'comment__in', 'meta_value', 'meta_value_num',
	 *                                                   the value of $meta_key, and the array keys of
	 *                                                   `$meta_query`. Also accepts false, an empty array, or
	 *                                                   'none' to disable `ORDER BY` clause.
	 *                                                   Default: 'comment_date_gmt'.
	 *     @type string       $order                     How to order retrieved comments. Accepts 'ASC', 'DESC'.
	 *                                                   Default: 'DESC'.
	 *     @type int          $parent                    Parent ID of comment to retrieve children of.
	 *                                                   Default empty.
	 *     @type array        $parent__in                Array of parent IDs of comments to retrieve children for.
	 *                                                   Default empty.
	 *     @type array        $parent__not_in            Array of parent IDs of comments *not* to retrieve
	 *                                                   children for. Default empty.
	 *     @type array        $post_author__in           Array of author IDs to retrieve comments for.
	 *                                                   Default empty.
	 *     @type array        $post_author__not_in       Array of author IDs *not* to retrieve comments for.
	 *                                                   Default empty.
	 *     @type int          $post_ID                   Currently unused.
	 *     @type int          $post_id                   Limit results to those affiliated with a given post ID.
	 *                                                   Default 0.
	 *     @type array        $post__in                  Array of post IDs to include affiliated comments for.
	 *                                                   Default empty.
	 *     @type array        $post__not_in              Array of post IDs to exclude affiliated comments for.
	 *                                                   Default empty.
	 *     @type int          $post_author               Post author ID to limit results by. Default empty.
	 *     @type string|array $post_status               Post status or array of post statuses to retrieve
	 *                                                   affiliated comments for. Pass 'any' to match any value.
	 *                                                   Default empty.
	 *     @type string       $post_type                 Post type or array of post types to retrieve affiliated
	 *                                                   comments for. Pass 'any' to match any value. Default empty.
	 *     @type string       $post_name                 Post name to retrieve affiliated comments for.
	 *                                                   Default empty.
	 *     @type int          $post_parent               Post parent ID to retrieve affiliated comments for.
	 *                                                   Default empty.
	 *     @type string       $search                    Search term(s) to retrieve matching comments for.
	 *                                                   Default empty.
	 *     @type string       $status                    Comment status to limit results by. Accepts 'hold'
	 *                                                   (`comment_status=0`), 'approve' (`comment_status=1`),
	 *                                                   'all', or a custom comment status. Default 'all'.
	 *     @type string|array $type                      Include comments of a given type, or array of types.
	 *                                                   Accepts 'comment', 'pings' (includes 'pingback' and
	 *                                                   'trackback'), or anycustom type string. Default empty.
	 *     @type array        $type__in                  Include comments from a given array of comment types.
	 *                                                   Default empty.
	 *     @type array        $type__not_in              Exclude comments from a given array of comment types.
	 *                                                   Default empty.
	 *     @type int          $user_id                   Include comments for a specific user ID. Default empty.
	 *     @type bool|string  $hierarchical              Whether to include comment descendants in the results.
	 *                                                   'threaded' returns a tree, with each comment's children
	 *                                                   stored in a `children` property on the `WP_Comment`
	 *                                                   object. 'flat' returns a flat array of found comments plus
	 *                                                   their children. Pass `false` to leave out descendants.
	 *                                                   The parameter is ignored (forced to `false`) when
	 *                                                   `$fields` is 'ids' or 'counts'. Accepts 'threaded',
	 *                                                   'flat', or false. Default: false.
 	 *     @type string       $cache_domain              Unique cache key to be produced when this query is stored in
	 *                                                   an object cache. Default is 'core'.
	 *     @type bool         $update_comment_meta_cache Whether to prime the metadata cache for found comments.
	 *                                                   Default true.
	 *     @type bool         $update_comment_post_cache Whether to prime the cache for comment posts.
	 *                                                   Default false.
	 * }
	 */
	public function __construct( $query = '' ) {
		$this->query_var_defaults = array(
			'author_email' => '',
			'author_url' => '',
			'author__in' => '',
			'author__not_in' => '',
			'include_unapproved' => '',
			'fields' => '',
			'ID' => '',
			'comment__in' => '',
			'comment__not_in' => '',
			'karma' => '',
			'number' => '',
			'offset' => '',
			'no_found_rows' => true,
			'orderby' => '',
			'order' => 'DESC',
			'paged' => 1,
			'parent' => '',
			'parent__in' => '',
			'parent__not_in' => '',
			'post_author__in' => '',
			'post_author__not_in' => '',
			'post_ID' => '',
			'post_id' => 0,
			'post__in' => '',
			'post__not_in' => '',
			'post_author' => '',
			'post_name' => '',
			'post_parent' => '',
			'post_status' => '',
			'post_type' => '',
			'status' => 'all',
			'type' => '',
			'type__in' => '',
			'type__not_in' => '',
			'user_id' => '',
			'search' => '',
			'count' => false,
			'meta_key' => '',
			'meta_value' => '',
			'meta_query' => '',
			'date_query' => null, // See WP_Date_Query
			'hierarchical' => false,
			'cache_domain' => 'core',
			'update_comment_meta_cache' => true,
			'update_comment_post_cache' => false,
		);

		if ( ! empty( $query ) ) {
			$this->query( $query );
		}
	}

	/**
	 * Parse arguments passed to the comment query with default query parameters.
	 *
	 * @since 4.2.0 Extracted from WP_Comment_Query::query().
	 *
	 *
	 * @param string|array $query WP_Comment_Query arguments. See WP_Comment_Query::__construct()
	 */
	public function parse_query( $query = '' ) {
		if ( empty( $query ) ) {
			$query = $this->query_vars;
		}

		$this->query_vars = wp_parse_args( $query, $this->query_var_defaults );

		/**
		 * Fires after the comment query vars have been parsed.
		 *
		 * @since 4.2.0
		 *
		 * @param WP_Comment_Query $this The WP_Comment_Query instance (passed by reference).
		 */
		do_action_ref_array( 'parse_comment_query', array( &$this ) );
	}

	/**
	 * Sets up the WordPress query for retrieving comments.
	 *
	 * @since 3.1.0
	 * @since 4.1.0 Introduced 'comment__in', 'comment__not_in', 'post_author__in',
	 *              'post_author__not_in', 'author__in', 'author__not_in', 'post__in',
	 *              'post__not_in', 'include_unapproved', 'type__in', and 'type__not_in'
	 *              arguments to $query_vars.
	 * @since 4.2.0 Moved parsing to WP_Comment_Query::parse_query().
	 *
	 * @param string|array $query Array or URL query string of parameters.
	 * @return array|int List of comments, or number of comments when 'count' is passed as a query var.
	 */
	public function query( $query ) {
		$this->query_vars = wp_parse_args( $query );
		return $this->get_comments();
	}

	/**
	 * Get a list of comments matching the query vars.
	 *
	 * @since 4.2.0
	 *
	 * @global wpdb $wpdb WordPress database abstraction object.
	 *
	 * @return int|array List of comments or number of found comments if `$count` argument is true.
	 */
	public function get_comments() {
		global $wpdb;

		$this->parse_query();

		// Parse meta query
		$this->meta_query = new WP_Meta_Query();
		$this->meta_query->parse_query_vars( $this->query_vars );

		/**
		 * Fires before comments are retrieved.
		 *
		 * @since 3.1.0
		 *
		 * @param WP_Comment_Query $this Current instance of WP_Comment_Query (passed by reference).
		 */
		do_action_ref_array( 'pre_get_comments', array( &$this ) );

		// Reparse query vars, in case they were modified in a 'pre_get_comments' callback.
		$this->meta_query->parse_query_vars( $this->query_vars );
		if ( ! empty( $this->meta_query->queries ) ) {
			$this->meta_query_clauses = $this->meta_query->get_sql( 'comment', $wpdb->comments, 'comment_ID', $this );
		}

		/*
		 * Only use the args defined in the query_var_defaults to compute the key,
		 * but ignore 'fields', which does not affect query results.
		 */
		$_args = wp_array_slice_assoc( $this->query_vars, array_keys( $this->query_var_defaults ) );
		unset( $_args['fields'] );

		$key = md5( serialize( $_args ) );
		$last_changed = wp_cache_get_last_changed( 'comment' );

		$cache_key   = "get_comments:$key:$last_changed";
		$cache_value = wp_cache_get( $cache_key, 'comment' );
		if ( false === $cache_value ) {
			$comment_ids = $this->get_comment_ids();
			if ( $comment_ids ) {
				$this->set_found_comments();
			}

			$cache_value = array(
				'comment_ids'    => $comment_ids,
				'found_comments' => $this->found_comments,
			);
			wp_cache_add( $cache_key, $cache_value, 'comment' );
		} else {
			$comment_ids          = $cache_value['comment_ids'];
			$this->found_comments = $cache_value['found_comments'];
		}

		if ( $this->found_comments && $this->query_vars['number'] ) {
			$this->max_num_pages = ceil( $this->found_comments / $this->query_vars['number'] );
		}

		// If querying for a count only, there's nothing more to do.
		if ( $this->query_vars['count'] ) {
			// $comment_ids is actually a count in this case.
			return intval( $comment_ids );
		}

		$comment_ids = array_map( 'intval', $comment_ids );

		if ( 'ids' == $this->query_vars['fields'] ) {
			$this->comments = $comment_ids;
			return $this->comments;
		}

		_prime_comment_caches( $comment_ids, $this->query_vars['update_comment_meta_cache'] );

		// Fetch full comment objects from the primed cache.
		$_comments = array();
		foreach ( $comment_ids as $comment_id ) {
			if ( $_comment = get_comment( $comment_id ) ) {
				$_comments[] = $_comment;
			}
		}

		// Prime comment post caches.
		if ( $this->query_vars['update_comment_post_cache'] ) {
			$comment_post_ids = array();
			foreach ( $_comments as $_comment ) {
				$comment_post_ids[] = $_comment->comment_post_ID;
			}

			_prime_post_caches( $comment_post_ids, false, false );
		}

		/**
		 * Filters the comment query results.
		 *
		 * @since 3.1.0
		 *
		 * @param array            $_comments An array of comments.
		 * @param WP_Comment_Query $this     Current instance of WP_Comment_Query (passed by reference).
		 */
		$_comments = apply_filters_ref_array( 'the_comments', array( $_comments, &$this ) );

		// Convert to WP_Comment instances
		$comments = array_map( 'get_comment', $_comments );

		if ( $this->query_vars['hierarchical'] ) {
			$comments = $this->fill_descendants( $comments );
		}

		$this->comments = $comments;
		return $this->comments;
	}

	/**
	 * Used internally to get a list of comment IDs matching the query vars.
	 *
	 * @since 4.4.0
	 *
	 * @global wpdb $wpdb WordPress database abstraction object.
	 */
	protected function get_comment_ids() {
		global $wpdb;

		// Assemble clauses related to 'comment_approved'.
		$approved_clauses = array();

		// 'status' accepts an array or a comma-separated string.
		$status_clauses = array();
		$statuses = $this->query_vars['status'];
		if ( ! is_array( $statuses ) ) {
			$statuses = preg_split( '/[\s,]+/', $statuses );
		}

		// 'any' overrides other statuses.
		if ( ! in_array( 'any', $statuses ) ) {
			foreach ( $statuses as $status ) {
				switch ( $status ) {
					case 'hold' :
						$status_clauses[] = "comment_approved = '0'";
						break;

					case 'approve' :
						$status_clauses[] = "comment_approved = '1'";
						break;

					case 'all' :
					case '' :
						$status_clauses[] = "( comment_approved = '0' OR comment_approved = '1' )";
						break;

					default :
						$status_clauses[] = $wpdb->prepare( "comment_approved = %s", $status );
						break;
				}
			}

			if ( ! empty( $status_clauses ) ) {
				$approved_clauses[] = '( ' . implode( ' OR ', $status_clauses ) . ' )';
			}
		}

		// User IDs or emails whose unapproved comments are included, regardless of $status.
		if ( ! empty( $this->query_vars['include_unapproved'] ) ) {
			$include_unapproved = $this->query_vars['include_unapproved'];

			// Accepts arrays or comma-separated strings.
			if ( ! is_array( $include_unapproved ) ) {
				$include_unapproved = preg_split( '/[\s,]+/', $include_unapproved );
			}

			$unapproved_ids = $unapproved_emails = array();
			foreach ( $include_unapproved as $unapproved_identifier ) {
				// Numeric values are assumed to be user ids.
				if ( is_numeric( $unapproved_identifier ) ) {
					$approved_clauses[] = $wpdb->prepare( "( user_id = %d AND comment_approved = '0' )", $unapproved_identifier );

				// Otherwise we match against email addresses.
				} else {
					$approved_clauses[] = $wpdb->prepare( "( comment_author_email = %s AND comment_approved = '0' )", $unapproved_identifier );
				}
			}
		}

		// Collapse comment_approved clauses into a single OR-separated clause.
		if ( ! empty( $approved_clauses ) ) {
			if ( 1 === count( $approved_clauses ) ) {
				$this->sql_clauses['where']['approved'] = $approved_clauses[0];
			} else {
				$this->sql_clauses['where']['approved'] = '( ' . implode( ' OR ', $approved_clauses ) . ' )';
			}
		}

		$order = ( 'ASC' == strtoupper( $this->query_vars['order'] ) ) ? 'ASC' : 'DESC';

		// Disable ORDER BY with 'none', an empty array, or boolean false.
		if ( in_array( $this->query_vars['orderby'], array( 'none', array(), false ), true ) ) {
			$orderby = '';
		} elseif ( ! empty( $this->query_vars['orderby'] ) ) {
			$ordersby = is_array( $this->query_vars['orderby'] ) ?
				$this->query_vars['orderby'] :
				preg_split( '/[,\s]/', $this->query_vars['orderby'] );

			$orderby_array = array();
			$found_orderby_comment_ID = false;
			foreach ( $ordersby as $_key => $_value ) {
				if ( ! $_value ) {
					continue;
				}

				if ( is_int( $_key ) ) {
					$_orderby = $_value;
					$_order = $order;
				} else {
					$_orderby = $_key;
					$_order = $_value;
				}

				if ( ! $found_orderby_comment_ID && in_array( $_orderby, array( 'comment_ID', 'comment__in' ) ) ) {
					$found_orderby_comment_ID = true;
				}

				$parsed = $this->parse_orderby( $_orderby );

				if ( ! $parsed ) {
					continue;
				}

				if ( 'comment__in' === $_orderby ) {
					$orderby_array[] = $parsed;
					continue;
				}

				$orderby_array[] = $parsed . ' ' . $this->parse_order( $_order );
			}

			// If no valid clauses were found, order by comment_date_gmt.
			if ( empty( $orderby_array ) ) {
				$orderby_array[] = "$wpdb->comments.comment_date_gmt $order";
			}

			// To ensure determinate sorting, always include a comment_ID clause.
			if ( ! $found_orderby_comment_ID ) {
				$comment_ID_order = '';

				// Inherit order from comment_date or comment_date_gmt, if available.
				foreach ( $orderby_array as $orderby_clause ) {
					if ( preg_match( '/comment_date(?:_gmt)*\ (ASC|DESC)/', $orderby_clause, $match ) ) {
						$comment_ID_order = $match[1];
						break;
					}
				}

				// If no date-related order is available, use the date from the first available clause.
				if ( ! $comment_ID_order ) {
					foreach ( $orderby_array as $orderby_clause ) {
						if ( false !== strpos( 'ASC', $orderby_clause ) ) {
							$comment_ID_order = 'ASC';
						} else {
							$comment_ID_order = 'DESC';
						}

						break;
					}
				}

				// Default to DESC.
				if ( ! $comment_ID_order ) {
					$comment_ID_order = 'DESC';
				}

				$orderby_array[] = "$wpdb->comments.comment_ID $comment_ID_order";
			}

			$orderby = implode( ', ', $orderby_array );
		} else {
			$orderby = "$wpdb->comments.comment_date_gmt $order";
		}

		$number = absint( $this->query_vars['number'] );
		$offset = absint( $this->query_vars['offset'] );
		$paged = absint( $this->query_vars['paged'] );

		if ( ! empty( $number ) ) {
			if ( $offset ) {
				$limits = 'LIMIT ' . $offset . ',' . $number;
			} else {
				$limits = 'LIMIT ' . ( $number * ( $paged - 1 ) ) . ',' . $number;
			}
		}

		if ( $this->query_vars['count'] ) {
			$fields = 'COUNT(*)';
		} else {
			$fields = "$wpdb->comments.comment_ID";
		}

		$post_id = absint( $this->query_vars['post_id'] );
		if ( ! empty( $post_id ) ) {
			$this->sql_clauses['where']['post_id'] = $wpdb->prepare( 'comment_post_ID = %d', $post_id );
		}

		// Parse comment IDs for an IN clause.
		if ( ! empty( $this->query_vars['comment__in'] ) ) {
			$this->sql_clauses['where']['comment__in'] = "$wpdb->comments.comment_ID IN ( " . implode( ',', wp_parse_id_list( $this->query_vars['comment__in'] ) ) . ' )';
		}

		// Parse comment IDs for a NOT IN clause.
		if ( ! empty( $this->query_vars['comment__not_in'] ) ) {
			$this->sql_clauses['where']['comment__not_in'] = "$wpdb->comments.comment_ID NOT IN ( " . implode( ',', wp_parse_id_list( $this->query_vars['comment__not_in'] ) ) . ' )';
		}

		// Parse comment parent IDs for an IN clause.
		if ( ! empty( $this->query_vars['parent__in'] ) ) {
			$this->sql_clauses['where']['parent__in'] = 'comment_parent IN ( ' . implode( ',', wp_parse_id_list( $this->query_vars['parent__in'] ) ) . ' )';
		}

		// Parse comment parent IDs for a NOT IN clause.
		if ( ! empty( $this->query_vars['parent__not_in'] ) ) {
			$this->sql_clauses['where']['parent__not_in'] = 'comment_parent NOT IN ( ' . implode( ',', wp_parse_id_list( $this->query_vars['parent__not_in'] ) ) . ' )';
		}

		// Parse comment post IDs for an IN clause.
		if ( ! empty( $this->query_vars['post__in'] ) ) {
			$this->sql_clauses['where']['post__in'] = 'comment_post_ID IN ( ' . implode( ',', wp_parse_id_list( $this->query_vars['post__in'] ) ) . ' )';
		}

		// Parse comment post IDs for a NOT IN clause.
		if ( ! empty( $this->query_vars['post__not_in'] ) ) {
			$this->sql_clauses['where']['post__not_in'] = 'comment_post_ID NOT IN ( ' . implode( ',', wp_parse_id_list( $this->query_vars['post__not_in'] ) ) . ' )';
		}

		if ( '' !== $this->query_vars['author_email'] ) {
			$this->sql_clauses['where']['author_email'] = $wpdb->prepare( 'comment_author_email = %s', $this->query_vars['author_email'] );
		}

		if ( '' !== $this->query_vars['author_url'] ) {
			$this->sql_clauses['where']['author_url'] = $wpdb->prepare( 'comment_author_url = %s', $this->query_vars['author_url'] );
		}

		if ( '' !== $this->query_vars['karma'] ) {
			$this->sql_clauses['where']['karma'] = $wpdb->prepare( 'comment_karma = %d', $this->query_vars['karma'] );
		}

		// Filtering by comment_type: 'type', 'type__in', 'type__not_in'.
		$raw_types = array(
			'IN' => array_merge( (array) $this->query_vars['type'], (array) $this->query_vars['type__in'] ),
			'NOT IN' => (array) $this->query_vars['type__not_in'],
		);

		$comment_types = array();
		foreach ( $raw_types as $operator => $_raw_types ) {
			$_raw_types = array_unique( $_raw_types );

			foreach ( $_raw_types as $type ) {
				switch ( $type ) {
					// An empty translates to 'all', for backward compatibility
					case '':
					case 'all' :
						break;

					case 'comment':
					case 'comments':
						$comment_types[ $operator ][] = "''";
						break;

					case 'pings':
						$comment_types[ $operator ][] = "'pingback'";
						$comment_types[ $operator ][] = "'trackback'";
						break;

					default:
						$comment_types[ $operator ][] = $wpdb->prepare( '%s', $type );
						break;
				}
			}

			if ( ! empty( $comment_types[ $operator ] ) ) {
				$types_sql = implode( ', ', $comment_types[ $operator ] );
				$this->sql_clauses['where']['comment_type__' . strtolower( str_replace( ' ', '_', $operator ) ) ] = "comment_type $operator ($types_sql)";
			}
		}

		$parent = $this->query_vars['parent'];
		if ( $this->query_vars['hierarchical'] && ! $parent ) {
			$parent = 0;
		}

		if ( '' !== $parent ) {
			$this->sql_clauses['where']['parent'] = $wpdb->prepare( 'comment_parent = %d', $parent );
		}

		if ( is_array( $this->query_vars['user_id'] ) ) {
			$this->sql_clauses['where']['user_id'] = 'user_id IN (' . implode( ',', array_map( 'absint', $this->query_vars['user_id'] ) ) . ')';
		} elseif ( '' !== $this->query_vars['user_id'] ) {
			$this->sql_clauses['where']['user_id'] = $wpdb->prepare( 'user_id = %d', $this->query_vars['user_id'] );
		}

		// Falsy search strings are ignored.
		if ( strlen( $this->query_vars['search'] ) ) {
			$search_sql = $this->get_search_sql(
				$this->query_vars['search'],
				array( 'comment_author', 'comment_author_email', 'comment_author_url', 'comment_author_IP', 'comment_content' )
			);

			// Strip leading 'AND'.
			$this->sql_clauses['where']['search'] = preg_replace( '/^\s*AND\s*/', '', $search_sql );
		}

		// If any post-related query vars are passed, join the posts table.
		$join_posts_table = false;
		$plucked = wp_array_slice_assoc( $this->query_vars, array( 'post_author', 'post_name', 'post_parent' ) );
		$post_fields = array_filter( $plucked );

		if ( ! empty( $post_fields ) ) {
			$join_posts_table = true;
			foreach ( $post_fields as $field_name => $field_value ) {
				// $field_value may be an array.
				$esses = array_fill( 0, count( (array) $field_value ), '%s' );
				$this->sql_clauses['where'][ $field_name ] = $wpdb->prepare( " {$wpdb->posts}.{$field_name} IN (" . implode( ',', $esses ) . ')', $field_value );
			}
		}

		// 'post_status' and 'post_type' are handled separately, due to the specialized behavior of 'any'.
		foreach ( array( 'post_status', 'post_type' ) as $field_name ) {
			$q_values = array();
			if ( ! empty( $this->query_vars[ $field_name ] ) ) {
				$q_values = $this->query_vars[ $field_name ];
				if ( ! is_array( $q_values ) ) {
					$q_values = explode( ',', $q_values );
				}

				// 'any' will cause the query var to be ignored.
				if ( in_array( 'any', $q_values, true ) || empty( $q_values ) ) {
					continue;
				}

				$join_posts_table = true;

				$esses = array_fill( 0, count( $q_values ), '%s' );
				$this->sql_clauses['where'][ $field_name ] = $wpdb->prepare( " {$wpdb->posts}.{$field_name} IN (" . implode( ',', $esses ) . ")", $q_values );
			}
		}

		// Comment author IDs for an IN clause.
		if ( ! empty( $this->query_vars['author__in'] ) ) {
			$this->sql_clauses['where']['author__in'] = 'user_id IN ( ' . implode( ',', wp_parse_id_list( $this->query_vars['author__in'] ) ) . ' )';
		}

		// Comment author IDs for a NOT IN clause.
		if ( ! empty( $this->query_vars['author__not_in'] ) ) {
			$this->sql_clauses['where']['author__not_in'] = 'user_id NOT IN ( ' . implode( ',', wp_parse_id_list( $this->query_vars['author__not_in'] ) ) . ' )';
		}

		// Post author IDs for an IN clause.
		if ( ! empty( $this->query_vars['post_author__in'] ) ) {
			$join_posts_table = true;
			$this->sql_clauses['where']['post_author__in'] = 'post_author IN ( ' . implode( ',', wp_parse_id_list( $this->query_vars['post_author__in'] ) ) . ' )';
		}

		// Post author IDs for a NOT IN clause.
		if ( ! empty( $this->query_vars['post_author__not_in'] ) ) {
			$join_posts_table = true;
			$this->sql_clauses['where']['post_author__not_in'] = 'post_author NOT IN ( ' . implode( ',', wp_parse_id_list( $this->query_vars['post_author__not_in'] ) ) . ' )';
		}

		$join = '';

		if ( $join_posts_table ) {
			$join .= "JOIN $wpdb->posts ON $wpdb->posts.ID = $wpdb->comments.comment_post_ID";
		}

		if ( ! empty( $this->meta_query_clauses ) ) {
			$join .= $this->meta_query_clauses['join'];

			// Strip leading 'AND'.
			$this->sql_clauses['where']['meta_query'] = preg_replace( '/^\s*AND\s*/', '', $this->meta_query_clauses['where'] );

			if ( ! $this->query_vars['count'] ) {
				$groupby = "{$wpdb->comments}.comment_ID";
			}
		}

		if ( ! empty( $this->query_vars['date_query'] ) && is_array( $this->query_vars['date_query'] ) ) {
			$this->date_query = new WP_Date_Query( $this->query_vars['date_query'], 'comment_date' );
			$this->sql_clauses['where']['date_query'] = preg_replace( '/^\s*AND\s*/', '', $this->date_query->get_sql() );
		}

		$where = implode( ' AND ', $this->sql_clauses['where'] );

		$pieces = array( 'fields', 'join', 'where', 'orderby', 'limits', 'groupby' );
		/**
		 * Filters the comment query clauses.
		 *
		 * @since 3.1.0
		 *
		 * @param array            $pieces A compacted array of comment query clauses.
		 * @param WP_Comment_Query $this  Current instance of WP_Comment_Query (passed by reference).
		 */
		$clauses = apply_filters_ref_array( 'comments_clauses', array( compact( $pieces ), &$this ) );

		$fields = isset( $clauses[ 'fields' ] ) ? $clauses[ 'fields' ] : '';
		$join = isset( $clauses[ 'join' ] ) ? $clauses[ 'join' ] : '';
		$where = isset( $clauses[ 'where' ] ) ? $clauses[ 'where' ] : '';
		$orderby = isset( $clauses[ 'orderby' ] ) ? $clauses[ 'orderby' ] : '';
		$limits = isset( $clauses[ 'limits' ] ) ? $clauses[ 'limits' ] : '';
		$groupby = isset( $clauses[ 'groupby' ] ) ? $clauses[ 'groupby' ] : '';

		$this->filtered_where_clause = $where;

		if ( $where ) {
			$where = 'WHERE ' . $where;
		}

		if ( $groupby ) {
			$groupby = 'GROUP BY ' . $groupby;
		}

		if ( $orderby ) {
			$orderby = "ORDER BY $orderby";
		}

		$found_rows = '';
		if ( ! $this->query_vars['no_found_rows'] ) {
			$found_rows = 'SQL_CALC_FOUND_ROWS';
		}

		$this->sql_clauses['select']  = "SELECT $found_rows $fields";
		$this->sql_clauses['from']    = "FROM $wpdb->comments $join";
		$this->sql_clauses['groupby'] = $groupby;
		$this->sql_clauses['orderby'] = $orderby;
		$this->sql_clauses['limits']  = $limits;

		$this->request = "{$this->sql_clauses['select']} {$this->sql_clauses['from']} {$where} {$this->sql_clauses['groupby']} {$this->sql_clauses['orderby']} {$this->sql_clauses['limits']}";

		if ( $this->query_vars['count'] ) {
			return intval( $wpdb->get_var( $this->request ) );
		} else {
			$comment_ids = $wpdb->get_col( $this->request );
			return array_map( 'intval', $comment_ids );
		}
	}

	/**
	 * Populates found_comments and max_num_pages properties for the current
	 * query if the limit clause was used.
	 *
	 * @since 4.6.0
	 *
	 * @global wpdb $wpdb WordPress database abstraction object.
	 */
	private function set_found_comments() {
		global $wpdb;

		if ( $this->query_vars['number'] && ! $this->query_vars['no_found_rows'] ) {
			/**
			 * Filters the query used to retrieve found comment count.
			 *
			 * @since 4.4.0
			 *
			 * @param string           $found_comments_query SQL query. Default 'SELECT FOUND_ROWS()'.
			 * @param WP_Comment_Query $comment_query        The `WP_Comment_Query` instance.
			 */
			$found_comments_query = apply_filters( 'found_comments_query', 'SELECT FOUND_ROWS()', $this );

			$this->found_comments = (int) $wpdb->get_var( $found_comments_query );
		}
	}

	/**
	 * Fetch descendants for located comments.
	 *
	 * Instead of calling `get_children()` separately on each child comment, we do a single set of queries to fetch
	 * the descendant trees for all matched top-level comments.
	 *
	 * @since 4.4.0
	 *
	 * @global wpdb $wpdb WordPress database abstraction object.
	 *
	 * @param array $comments Array of top-level comments whose descendants should be filled in.
	 * @return array
	 */
	protected function fill_descendants( $comments ) {
		global $wpdb;

		$levels = array(
			0 => wp_list_pluck( $comments, 'comment_ID' ),
		);

		$key = md5( serialize( wp_array_slice_assoc( $this->query_vars, array_keys( $this->query_var_defaults ) ) ) );
		$last_changed = wp_cache_get_last_changed( 'comment' );

		// Fetch an entire level of the descendant tree at a time.
		$level = 0;
		$exclude_keys = array( 'parent', 'parent__in', 'parent__not_in' );
		do {
			// Parent-child relationships may be cached. Only query for those that are not.
			$child_ids = $uncached_parent_ids = array();
			$_parent_ids = $levels[ $level ];
			foreach ( $_parent_ids as $parent_id ) {
				$cache_key = "get_comment_child_ids:$parent_id:$key:$last_changed";
				$parent_child_ids = wp_cache_get( $cache_key, 'comment' );
				if ( false !== $parent_child_ids ) {
					$child_ids = array_merge( $child_ids, $parent_child_ids );
				} else {
					$uncached_parent_ids[] = $parent_id;
				}
			}

			if ( $uncached_parent_ids ) {
				// Fetch this level of comments.
				$parent_query_args = $this->query_vars;
				foreach ( $exclude_keys as $exclude_key ) {
					$parent_query_args[ $exclude_key ] = '';
				}
				$parent_query_args['parent__in']    = $uncached_parent_ids;
				$parent_query_args['no_found_rows'] = true;
				$parent_query_args['hierarchical']  = false;
				$parent_query_args['offset']        = 0;
				$parent_query_args['number']        = 0;

				$level_comments = get_comments( $parent_query_args );

				// Cache parent-child relationships.
				$parent_map = array_fill_keys( $uncached_parent_ids, array() );
				foreach ( $level_comments as $level_comment ) {
					$parent_map[ $level_comment->comment_parent ][] = $level_comment->comment_ID;
					$child_ids[] = $level_comment->comment_ID;
				}

				foreach ( $parent_map as $parent_id => $children ) {
					$cache_key = "get_comment_child_ids:$parent_id:$key:$last_changed";
					wp_cache_set( $cache_key, $children, 'comment' );
				}
			}

			$level++;
			$levels[ $level ] = $child_ids;
		} while ( $child_ids );

		// Prime comment caches for non-top-level comments.
		$descendant_ids = array();
		for ( $i = 1, $c = count( $levels ); $i < $c; $i++ ) {
			$descendant_ids = array_merge( $descendant_ids, $levels[ $i ] );
		}

		_prime_comment_caches( $descendant_ids, $this->query_vars['update_comment_meta_cache'] );

		// Assemble a flat array of all comments + descendants.
		$all_comments = $comments;
		foreach ( $descendant_ids as $descendant_id ) {
			$all_comments[] = get_comment( $descendant_id );
		}

		// If a threaded representation was requested, build the tree.
		if ( 'threaded' === $this->query_vars['hierarchical'] ) {
			$threaded_comments = $ref = array();
			foreach ( $all_comments as $k => $c ) {
				$_c = get_comment( $c->comment_ID );

				// If the comment isn't in the reference array, it goes in the top level of the thread.
				if ( ! isset( $ref[ $c->comment_parent ] ) ) {
					$threaded_comments[ $_c->comment_ID ] = $_c;
					$ref[ $_c->comment_ID ] = $threaded_comments[ $_c->comment_ID ];

				// Otherwise, set it as a child of its parent.
				} else {

					$ref[ $_c->comment_parent ]->add_child( $_c );
					$ref[ $_c->comment_ID ] = $ref[ $_c->comment_parent ]->get_child( $_c->comment_ID );
				}
			}

			// Set the 'populated_children' flag, to ensure additional database queries aren't run.
			foreach ( $ref as $_ref ) {
				$_ref->populated_children( true );
			}

			$comments = $threaded_comments;
		} else {
			$comments = $all_comments;
		}

		return $comments;
	}

	/**
	 * Used internally to generate an SQL string for searching across multiple columns
	 *
	 * @since 3.1.0
	 *
	 * @global wpdb $wpdb WordPress database abstraction object.
	 *
	 * @param string $string
	 * @param array $cols
	 * @return string
	 */
	protected function get_search_sql( $string, $cols ) {
		global $wpdb;

		$like = '%' . $wpdb->esc_like( $string ) . '%';

		$searches = array();
		foreach ( $cols as $col ) {
			$searches[] = $wpdb->prepare( "$col LIKE %s", $like );
		}

		return ' AND (' . implode(' OR ', $searches) . ')';
	}

	/**
	 * Parse and sanitize 'orderby' keys passed to the comment query.
	 *
	 * @since 4.2.0
	 *
	 * @global wpdb $wpdb WordPress database abstraction object.
	 *
	 * @param string $orderby Alias for the field to order by.
	 * @return string|false Value to used in the ORDER clause. False otherwise.
	 */
	protected function parse_orderby( $orderby ) {
		global $wpdb;

		$allowed_keys = array(
			'comment_agent',
			'comment_approved',
			'comment_author',
			'comment_author_email',
			'comment_author_IP',
			'comment_author_url',
			'comment_content',
			'comment_date',
			'comment_date_gmt',
			'comment_ID',
			'comment_karma',
			'comment_parent',
			'comment_post_ID',
			'comment_type',
			'user_id',
		);

		if ( ! empty( $this->query_vars['meta_key'] ) ) {
			$allowed_keys[] = $this->query_vars['meta_key'];
			$allowed_keys[] = 'meta_value';
			$allowed_keys[] = 'meta_value_num';
		}

		$meta_query_clauses = $this->meta_query->get_clauses();
		if ( $meta_query_clauses ) {
			$allowed_keys = array_merge( $allowed_keys, array_keys( $meta_query_clauses ) );
		}

		$parsed = false;
		if ( $orderby == $this->query_vars['meta_key'] || $orderby == 'meta_value' ) {
			$parsed = "$wpdb->commentmeta.meta_value";
		} elseif ( $orderby == 'meta_value_num' ) {
			$parsed = "$wpdb->commentmeta.meta_value+0";
		} elseif ( $orderby == 'comment__in' ) {
			$comment__in = implode( ',', array_map( 'absint', $this->query_vars['comment__in'] ) );
			$parsed = "FIELD( {$wpdb->comments}.comment_ID, $comment__in )";
		} elseif ( in_array( $orderby, $allowed_keys ) ) {

			if ( isset( $meta_query_clauses[ $orderby ] ) ) {
				$meta_clause = $meta_query_clauses[ $orderby ];
				$parsed = sprintf( "CAST(%s.meta_value AS %s)", esc_sql( $meta_clause['alias'] ), esc_sql( $meta_clause['cast'] ) );
			} else {
				$parsed = "$wpdb->comments.$orderby";
			}
		}

		return $parsed;
	}

	/**
	 * Parse an 'order' query variable and cast it to ASC or DESC as necessary.
	 *
	 * @since 4.2.0
	 *
	 * @param string $order The 'order' query variable.
	 * @return string The sanitized 'order' query variable.
	 */
	protected function parse_order( $order ) {
		if ( ! is_string( $order ) || empty( $order ) ) {
			return 'DESC';
		}

		if ( 'ASC' === strtoupper( $order ) ) {
			return 'ASC';
		} else {
			return 'DESC';
		}
	}
}