mysql中去除左空格函数：
例子：
mysql中去除右空格函数：
例3：
this function is multi-byte safe.
trim函数可以过滤指定的字符串：
完整格式：trim([{both | leading | trailing} [remstr] from] str)
简化格式：trim([remstr from] str)
returns the string str with all remstr prefixes or suffixes removed. if none of the specifiers both, leading, or trailing is given, both is assumed. remstr is optional and, if not specified, spaces are removed.
mysql trim函数的例子：
mysql> select trim(' bar '); //默认删除前后空格
-> 'bar'
mysql> select trim(leading '，' from '，，barxxx'); //删除指定首字符 如’，‘
-> 'barxxx'
mysql> select trim(both '，' from '，，bar，，，'); //删除指定首尾字符
-> 'bar'
mysql> select trim(trailing '，' from 'barxxyz，，');
-> 'barxxyz'
mysql> update table set `field`=trim(trailing ',' from `field`) where where `field` like '%,';
this function is multi-byte safe.