MySQL 字符串大小写转化函数

MySQL 字符串大小写转化函数有两对： lower(), uppper() 和 lcase(), ucase()：

mysql> select lower('AAA');  
+--------------+  
| lower('AAA') |  
+--------------+  
| aaa          |  
+--------------+  
mysql> select upper('aaa');  
+--------------+  
|upper('aaa') |  
+--------------+  
| AAA          |  
+--------------+  
mysql> select lcase('AAA');  
+--------------+  
| lcase('AAA') |  
+--------------+  
| aaa          |  
+--------------+  
mysql> select ucase('aaa');  
+--------------+  
| ucase('aaa') |  
+--------------+  
| AAA          |  
+--------------+