gistfile1.php

<?php
 
/**
 * Copy the data from one field to another, and delete the old field.
 */
function merge_fields($old_field, $new_field, $entity_type = '', $bundle = '') {
  $prefixes = array(
    'field_data_',
    'field_revision_',
  );
  foreach ($prefixes as $prefix) {
    $query = db_select($prefix . $old_field, 'old_field')
      ->fields('old_field');
 
    if (!empty($entity_type) && !empty($bundle)) {
      $query->condition('old_field.entity_type', $entity_type);
      $query->condition('old_field.bundle', $bundle);
    }
    $results = $query->execute();
 
    while ($row = $results->fetchAssoc()) {
      // Replace columns that are prefixed with field name.
      foreach ($row as $idx => $value) {
        if (strstr($idx, $old_field)) {
          $row[str_replace($old_field, $new_field, $idx)] = $value;
          unset($row[$idx]);
        }
      }
 
      db_insert($prefix . $new_field)
        ->fields($row)
        ->execute();
    }
  }
 
  if (!empty($entity_type) && !empty($bundle)) {
    field_delete_instance(array(
      'field_name' => $old_field,
      'entity_type' => $entity_type,
      'bundle' => $bundle,
    ));
 
    field_create_instance(array(
      'field_name' => $new_field,
      'entity_type' => $entity_type,
      'bundle' => $bundle,
    ));
  }
}