LPAD(str,len,padstr)

返回字符串str，左填充用字符串str中墊到len字符長度。如果str為大於len，返回值被縮短至len個字符。

SQL> SELECT LPAD('hi',4,'??');
+---------------------------------------------------------+
| LPAD('hi',4,'??')                                       |
+---------------------------------------------------------+
| ??hi                                                    |
+---------------------------------------------------------+
1 row in set (0.00 sec)