CHARSET(str)                     //返回字串字符集
CONCAT (string2  [,… ])     //连接字串，注意不要沿用ORACLE习惯

mysql> select concat('a','b');
+-----------------+
| concat('a','b') |
+-----------------+
| ab              |
+-----------------+
1 row in set (0.03 sec)

mysql> select 'a'||'b';
+----------+
| 'a'||'b' |
+----------+
|        0 |
+----------+
1 row in set, 2 warnings (0.00 sec)

INSTR (string ,substring )     //返回substring首次在string中出现的位置,不存在返回0
LCASE (string2 )                 //转换成小写
LEFT (string2 ,length )         //从string2中的左起取length个字符
LENGTH (string )                 //string长度
LOAD_FILE (file_name )         //从文件读取内容
LOCATE (substring , string  [,start_position ] )
//同INSTR,但可指定开始位置
LPAD (string2 ,length ,pad ) //重复用pad加在string开头,直到字串长度
为length
LTRIM (string2 )                 //去除前端空格
REPEAT (string2 ,count )     //重复count次
REPLACE (str ,search_str ,replace_str )
//在str中用replace_str替换search_str
RPAD (string2 ,length ,pad)  //在str后用pad补充,直到长度length
RTRIM (string2 )                    //去除后端空格
STRCMP (string1 ,string2 )   //逐字符比较两字串大小,
SUBSTRING (str , position  [,length ])
//从str的position开始,取length个字符

mysql> select substring('abcd',0,2);
+-----------------------+
| substring('abcd',0,2) |
+-----------------------+
|                       |
+-----------------------+
1 row in set (0.06 sec)

mysql> select substring('abcd',1,2);
+-----------------------+
| substring('abcd',1,2) |
+-----------------------+
| ab                    |
+-----------------------+
1 row in set (0.00 sec)

TRIM([[BOTH|LEADING|TRAILING] [padding] FROM]string2)
//去除指定位置的指定字符
UCASE (string2 )                 //转换成大写
RIGHT(string2,length)         //取string2最后length个字符
SPACE(count)                     //生成count个空格