Unable to AES_DECRYPT after AES_ENCRYPT in mysql

According to the Manual:

AES_ENCRYPT() encrypts a string and returns a binary string.
AES_DECRYPT() decrypts the encrypted string and returns the original string.

• MySQL 5.1 Doc: AES_ENCRYPT() / AES_DECRYPT()

I don’t know why it is still returning a binary string in your case. Anyway, try this:

SELECT *, 
       CAST(AES_DECRYPT(first_name, 'usa2010') AS CHAR(50)) first_name_decrypt 
FROM   user

And use first_name_decrypt instead of first_name.