Key-value storage for comment metadata. Extends comments with custom data.

Schema

Indexes

Foreign Key Relationships

• comment_id → wp_comments.comment_ID

Common Use Cases

Comment meta is used for:

• Spam scores – Akismet confidence levels
• Ratings – Star ratings attached to comments
• Voting – Upvotes/downvotes
• Moderation flags – Reports, review notes
• Plugin data – Subscription preferences, notification settings

Common Meta Keys

Common Queries

Get all meta for a comment

SELECT meta_key, meta_value 
FROM wp_commentmeta 
WHERE comment_id = 456;

Get specific meta value

SELECT meta_value 
FROM wp_commentmeta 
WHERE comment_id = 456 
  AND meta_key = 'rating';

Get comments with ratings

SELECT c.*, cm.meta_value as rating
FROM wp_comments c
JOIN wp_commentmeta cm ON c.comment_ID = cm.comment_id
WHERE cm.meta_key = 'rating'
  AND c.comment_approved = '1'
ORDER BY CAST(cm.meta_value AS SIGNED) DESC;

Calculate average rating for a post

SELECT 
  c.comment_post_ID,
  AVG(CAST(cm.meta_value AS DECIMAL)) as avg_rating,
  COUNT(*) as review_count
FROM wp_comments c
JOIN wp_commentmeta cm ON c.comment_ID = cm.comment_id
WHERE cm.meta_key = 'rating'
  AND c.comment_approved = '1'
GROUP BY c.comment_post_ID;

Delete orphaned commentmeta

DELETE cm FROM wp_commentmeta cm
LEFT JOIN wp_comments c ON cm.comment_id = c.comment_ID
WHERE c.comment_ID IS NULL;

WordPress API Functions

• get_comment_meta( $comment_id, $key, $single ) – Get meta value(s)
• add_comment_meta( $comment_id, $key, $value, $unique ) – Add meta
• update_comment_meta( $comment_id, $key, $value ) – Update meta
• delete_comment_meta( $comment_id, $key, $value ) – Delete meta

Example: Comment Ratings

// Save rating with comment
add_action( 'comment_post', function( $comment_id ) {
    if ( isset( $_POST['rating'] ) ) {
        $rating = intval( $_POST['rating'] );
        if ( $rating >= 1 && $rating <= 5 ) {
            add_comment_meta( $comment_id, 'rating', $rating, true );
        }
    }
});

// Display rating
$rating = get_comment_meta( $comment_id, 'rating', true );
if ( $rating ) {
    echo str_repeat( '★', $rating ) . str_repeat( '☆', 5 - $rating );
}

Performance Notes

• Comment meta table is often small compared to postmeta
• Spam comments can accumulate meta from anti-spam plugins
• Clean orphaned meta when bulk-deleting spam