Update Asset Index SQL Error
That error indicates a problem with the data in your database.

The craft_assetfolders table has a parentId column that is a foreign key reference to its own id column.  For whatever reason, that parentId column has a value that doesn't exist in any of the id columns, hence your errors.

Some common causes include:


Someone manually editing database values.
A botched import/export script when backing up/restoring databases.
Having multiple Craft installs (maybe across environments) pointing to the same cloud based Asset source (S3, Google Cloud, etc.) and someone deletes/moves/etc. an Asset on one environment making the other one out of sync with reality.