Answers.Body: <p>You can do it with the API explorer. Go to <strong>Support -&gt; Developer -&gt; API Explorer v4</strong> and enter settings exactly like this, except the three places where I refer to &quot;constituent_information.my_id_field&quot; you need to change it with the <em>exact</em> identifier of your custom field (to make sure you got it right, pick it from the &quot;Add Select&quot; list and then you can copy-paste it into the &quot;chain&quot; section):</p>
  <p><a href="https://i.sstatic.net/1ZZbt.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/1ZZbt.png" alt="APIv4 Explorer" /></a></p>
  <p>PS the code in that &quot;chain&quot; section is a lot so here it is for you to copy (this part needs a dollar sign before the name of your field, but the Select section does not):</p>
  <pre><code>{where: [[id, =, $id]], values: {external_identifier: $constituent_information.my_id_field}}
  </code></pre>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2024-01-19T20:30:01.190Z
Answers.LastActivityDate: 2024-01-19T20:30:01.190Z
Answers.UserDisplayName: Coleman
Body: <p>Loving civicrm, just getting to grips with it. I've imported a load of contacts but I've made a rookie error and instead of importing my unique ID number for each contact into the 'external_identifier' field I created my own custom field and imported it there. Unfortunately, I have so many contacts the Surname/First Name are not unique, only the custom unique ID is truly the way to distinguish individual contacts from each other. Is there a way to copy all the data across from my custom unique ID field to 'external_identifier'? I've tried doing this with a SQL query in phpmyadmin but having no luck.</p>
  
Tags: <custom-fields><external-id>
Title: Copy the contents of Custom Field to external_identfier field for all contacts
ThreadText: # Copy the contents of Custom Field to external_identfier field for all contacts
  
  (Asked by: username_0 on 2024-01-19)
  
  Loving civicrm, just getting to grips with it. I've imported a load of contacts but I've made a rookie error and instead of importing my unique ID number for each contact into the 'external\_identifier' field I created my own custom field and imported it there. Unfortunately, I have so many contacts the Surname/First Name are not unique, only the custom unique ID is truly the way to distinguish individual contacts from each other. Is there a way to copy all the data across from my custom unique ID field to 'external\_identifier'? I've tried doing this with a SQL query in phpmyadmin but having no luck.
  
  **Tags:** custom-fields, external-id
  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_1 on 2024-01-19. Score: 2 | Accepted answer
  
  You can do it with the API explorer. Go to **Support -> Developer -> API Explorer v4** and enter settings exactly like this, except the three places where I refer to "constituent\_information.my\_id\_field" you need to change it with the *exact* identifier of your custom field (to make sure you got it right, pick it from the "Add Select" list and then you can copy-paste it into the "chain" section):
  
  [![APIv4 Explorer](https://i.sstatic.net/1ZZbt.png)](https://i.sstatic.net/1ZZbt.png)
  
  PS the code in that "chain" section is a lot so here it is for you to copy (this part needs a dollar sign before the name of your field, but the Select section does not):
  
  ```
  {where: [[id, =, $id]], values: {external_identifier: $constituent_information.my_id_field}}
  
  ```
  
  
  ---
  
  