At our agency, we carried out an update from TYPO3 v8 to TYPO3 v9. The template used was based on the TYPO3 extension gridelements. After the update, however, some elements in the website's frontend were styled incorrectly. In the website backend, it was apparent that the corresponding element layout was incorrectly configured under the "Appearance" tab. The reason for this is that the layout field in the tt_content table is modified during the core update.
In this case, we need to back up the layout column from the old database and then transfer it to the new database using UPDATE statements. First, we therefore read out the layout column using the following command:
SELECT CONCAT('UPDATE tt_content set layout=',layout,' where uid=',uid,' limit 1;') FROM tt_content ORDER BY uid;
This gives us a set of convenient MySQL UPDATE statements for each content element, which we can then use to update the new tt_content table. The original layouts are restored as a result.
Encountered at our web agency on a website running TYPO3 9.5.19.
