加密解密函数

加密解密：
--------------
select AES_ENCRYPT(a,3),b from test3151
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+------------------+-------+
| AES_ENCRYPT(a,3) | b     |
+------------------+-------+
| G呣鋬昆邟飥            | world |
+------------------+-------+
1 row in set (Elapsed: 00:00:00.01)

--------------
select AES_DECRYPT(AES_ENCRYPT(a,3),3),b from test3151
--------------

+---------------------------------+-------+
| AES_DECRYPT(AES_ENCRYPT(a,3),3) | b     |
+---------------------------------+-------+
| hello                           | world |
+---------------------------------+-------+
1 row in set (Elapsed: 00:00:00.00)