create master key encryption by password = '123456'

create symmetric key [my] with algorithm = aes_256 encryption by password = '123456'


create table [my_table] (
id int,
num varbinary(max)
)


open symmetric key [my] decryption by password = '123456'
insert into my_table values (1, ENCRYPTBYKEY(key_guid('my'), '110'))
insert into my_table values (1, ENCRYPTBYKEY(key_guid('my'), '2000'))


alter table [my_table] add 
num_dec as convert(varchar(10), decryptbyKey(num))


select * from my_table

alter table my_table drop column num_dec;

sp_rename 'my_table.num', 'num2'

alter table [my_table] add 
num_dec as convert(varchar(10), decryptbyKey(num2))


select * from my_table

ALTER TABLE BankAccount
    ADD NumberDecrypted AS CONVERT(nvarchar(9), DecryptByKey(CONVERT(varbinary(300), Num)))