达梦语法：select concat('XXXXXX-',concat(REPLICATE(0,6-len(post_id)),post_id)) from sys_post ;
Mysql 语法1：SELECT CONCAT(REPEAT('0', 6 - LENGTH(post_id)), post_id) FROM sys_post;
Mysql 语法2：SELECT LPAD(post_id, 6, '0') FROM sys_post;
