Answers.Body: <p>Assuming you're running Craft version 3.4.27 or earlier, most likely your web host has updated MySQL and you're running into this issue: <a href="https://github.com/craftcms/cms/issues/6379" rel="nofollow noreferrer">https://github.com/craftcms/cms/issues/6379</a></p>
  <p>The fix is to update Craft to 3.4.28 or later (for security reasons; ideally to the latest 3.9.x release or even to Craft 4 as Craft 3 is EOL as of April 2024). Alternatively, you'll need to ensure MySQL is using a version prior to 8.0.21, or move to MariaDB.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2024-07-03T23:23:48.067Z
Answers.Text: Hi Mats,
  
  That makes sense. My hosting provider swore that they hadn't changed anything on the server when I contacted them about this the other day, but I bet they have (ggrrhh). I'll check it out tomorrow (it's gone midnight here in the UK).
  
  Thanks
  
  Philip
Answers.UserDisplayName: Philip Buckley
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2024-07-04T21:43:15.953Z
Answers.Text: Hi Mats, you were EXACTLY right. My hosting provider had (without warning) updated MySQL to 8.0.36. The site is now working again. Again, thankyou very much – there’s no way I would have been able to figure the problem out on my own. Philip
Answers.UserDisplayName: Philip Buckley
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2024-07-06T21:23:29.617Z
Answers.Text: @PhilipBuckley Awesome that I could help out! Hope you got it sorted, one way or the other :)
Answers.UserDisplayName: Mats Mikkel Rummelhoff
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2024-07-03T21:31:26.837Z
Answers.LastActivityDate: 2024-07-03T21:31:26.837Z
Answers.UserDisplayName: Mats Mikkel Rummelhoff
Body: <p>I built a site with Craft 3 in 2018. I have barely touched it since (or worked with Craft, to be honest). The front-end is fine and the end-users have been using it without problem until last week when they contacted me because they suddenly could not login to the back-end. I too cannot login. The login page is showing an Internal Server Error message. I have temporarily set ENVIRONMENT=“dev” in the .env file to see what the error message is. What I am seeing is:</p>
  <pre><code>PHP Notice – yiibaseErrorException
      
  Undefined index: constraint_name
      
  1. in /home/customer/www/cornerstonebooks.co.uk/vendor/yiisoft/yii2/db/mysql/Schema.php   at line 387 
  </code></pre>
  <p>etc. etc.</p>
  <p>I have absolutely no idea what that means or, more importantly, how to troubleshoot/fix it. Any suggestions as to how to go about fixing the problem, would be gratefully received.</p>
  <p>Thanks</p>
  <p>Philip</p>
  
Tags: <craft3><error>
Title: Craft 3 site – users suddenly cannot login to back-end
ThreadText: # Craft 3 site – users suddenly cannot login to back-end
  
  (Asked by: username_0 on 2024-07-03)
  
  I built a site with Craft 3 in 2018. I have barely touched it since (or worked with Craft, to be honest). The front-end is fine and the end-users have been using it without problem until last week when they contacted me because they suddenly could not login to the back-end. I too cannot login. The login page is showing an Internal Server Error message. I have temporarily set ENVIRONMENT=“dev” in the .env file to see what the error message is. What I am seeing is:
  
  ```
  PHP Notice – yiibaseErrorException
      
  Undefined index: constraint_name
      
  1. in /home/customer/www/cornerstonebooks.co.uk/vendor/yiisoft/yii2/db/mysql/Schema.php   at line 387 
  
  ```
  
  etc. etc.
  
  I have absolutely no idea what that means or, more importantly, how to troubleshoot/fix it. Any suggestions as to how to go about fixing the problem, would be gratefully received.
  
  Thanks
  
  username_0
  
  **Tags:** craft3, error
  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_1 on 2024-07-03. Score: 1 | Accepted answer
  
  Assuming you're running Craft version 3.4.27 or earlier, most likely your web host has updated MySQL and you're running into this issue: <https://github.com/craftcms/cms/issues/6379>
  
  The fix is to update Craft to 3.4.28 or later (for security reasons; ideally to the latest 3.9.x release or even to Craft 4 as Craft 3 is EOL as of April 2024). Alternatively, you'll need to ensure MySQL is using a version prior to 8.0.21, or move to MariaDB.
  
  > **Comments:**
  > **username_0**: Hi username_1,  That makes sense. My hosting provider swore that they hadn't changed anything on the server when I contacted them about this the other day, but I bet they have (ggrrhh). I'll check it out tomorrow (it's gone midnight here in the UK).  Thanks  username_0  
  > **username_0**: Hi username_1, you were EXACTLY right. My hosting provider had (without warning) updated MySQL to 8.0.36. The site is now working again. Again, thankyou very much – there’s no way I would have been able to figure the problem out on my own. username_0  
  > **username_1**: @username_0 Awesome that I could help out! Hope you got it sorted, one way or the other :)  
  
  ---
  
  