symmetric encryption sqlserver

The CREATE the SYMMETRIC KEY ZXC the WITH the ALGORITHM = AES_256 the ENCRYPTION BY PASSWORD =  ' ZXC123456 '   
- creating keys 

the OPEN the SYMMETRIC KEY ZXC the DECRYPTION BY PASSWORD =  ' ZXC123456 '    - open keys 

the SELECT  the CONVERT ( VARCHAR ( 10 ), DecryptByKey (the EncryptByKey (Key_guid ( ' ZXC ' ), ' YHDH_C ' ))) - set encryption 
CLOSE SYMMETRIC KEY ZXC;
DROP SYMMETRIC KEY ZXC;