WordPress at a glance
function is not described

comment_exists() WP 2.0.0

Determine if a comment exists based on author and date.

For best performance, use $timezone = 'gmt', which queries a field that is properly indexed. The default value for $timezone is 'blog' for legacy reasons.

  • Global. wpdb. $wpdb WordPress database abstraction object.
  • Since 4.4.0 Added the $timezone parameter.

No Hooks.

Return

Mixed. Comment post ID on success.

Usage

comment_exists( $comment_author, $comment_date, $timezone );
$comment_author(string) (required)
Author of the comment.
$comment_date(string) (required)
Date of the comment.
$timezone(string)
Timezone. Accepts 'blog' or 'gmt'.
Default: 'blog'

Code of comment exists: wp-admin/includes/comment.php VER 5.0.3

<?php
function comment_exists( $comment_author, $comment_date, $timezone = 'blog' ) {
	global $wpdb;

	$date_field = 'comment_date';
	if ( 'gmt' === $timezone ) {
		$date_field = 'comment_date_gmt';
	}

	return $wpdb->get_var( $wpdb->prepare("SELECT comment_post_ID FROM $wpdb->comments
			WHERE comment_author = %s AND $date_field = %s",
			stripslashes( $comment_author ),
			stripslashes( $comment_date )
	) );
}