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I have migrated my blog from blogspot to WordPress. Then I have noticed many of the posts contain duplicate custom fields. Like blogger_author, blogger_permalink, blogger_blog are duplicated upto 5 times. How can I remove the duplicate Custom Fields?

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up vote 5 down vote accepted

You can delete directly from the database, using an SQL statement like:

delete from wp_postmeta
where meta_id in (
       select *
       from (
               select meta_id
               from wp_postmeta a
               where a.meta_key = 'blogger_blog'
               and meta_id not in (
                       select min(meta_id)
                       from wp_postmeta b
                       where b.post_id = a.post_id
                       and b.meta_key = 'blogger_blog'
               )
       ) as x
);

Don't forget to change name of the meta_key on both places if you want to delete duplicates for another custom field.

or you can use a php script for this. Example:

 <?php
define('WP_USE_THEMES', false);
require('wp-blog-header.php');

    define( 'WP_DEBUG_DISPLAY', true ); 
    ini_set( 'display_errors', true );
    $allposts = get_posts('numberposts=-1&post_type=post&post_status=any');
    $keys = array('blogger_blog', 'blogger_author', 'blogger_permalink');
    foreach ( $keys as $key ) {
        foreach( $allposts as $postinfo) {
            // Fetch array of custom field values
            $postmeta = get_post_meta($postinfo->ID, $key);

            if (!empty($postmeta) ) {
                // Delete the custom field for this post (all occurrences)
                delete_post_meta($postinfo->ID, $key);

                // Insert one and only one custom field
                update_post_meta($postinfo->ID, $key, $postmeta[0]);
            }
        }
    }
?>
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It should be noted that this deletes all duplicate keys, not duplicate content. So if you have multiple custom fields with the key of "blogger_author" that are each different, only one of them will be saved. Just so you are aware.

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