When the optimizedb utility is used to create statistics for encrypted columns, the histogram cells will contain unencrypted (plain text) data. The histogram cells are statistical extracts and cannot be linked back to a specific row in the table (except when there is only a single table row). Nevertheless, depending on the nature of the data and your business, this may be considered a security breach.

If columns should be excluded, then the optimizedb -r (relation) and -a (attribute) flags can be used to specify which tables and columns to generate statistics for.

You can use the statdump command to verify which columns have had statistics generated for them.