You probably have to shrink it, but then you'll have to rebuild all the indexes... Good thing it's Friday... might be done by Monday.

Did you try using a CASE statement?

If you don't use a date in tabular model, you can't mark the column as a date, so you can't use a lot of the built in time intelligence functions......

A cursor for that is all kinds of overkill. How about a simple not exists subquery?

SELECT *
FROM Employee e
WHERE NOT EXISTS (
                    SELECT s.EmployeeID

(Wait, so you can update directly?)

Found this: https://docs.microsoft.com/en-us/sql/relational-databases/security/encryption/encrypt-a-column-of-data?view=sql-server-2017

Wouldn't you have to run this on each column?
UPDATE HumanResources.Employee SET EncryptedNationalIDNumber = EncryptByKey(Key_GUID('SSN_Key_01'), NationalIDNumber); 

You mean by querying the sys.all_columns table and using dynamic SQL to automate it?

Also, how do you fix a "slow database" when you don't know exactly what is slow? Do you have benchmarks? A list of the most used stored procedures?

Of course, if you want to recover the records you deleted, and you're in Simple Recovery, you're out of luck. You'd have to restore an old copy of the database...

???

Recovery models don't have anything to do with what SQL works in a database. That's controlled by the Compatibility Level the database is set to.

A data warehouse is just another database with a star schema instead of a standard 3NF schema.