oracle 中
select user_id ||'.'||user_name as name from user_list;
sqlserver中
select user_id +'.'+ user_name as name from user_list;
类型不一致的情况,user_id 为 decimal user_name 为 varchar
select CONVERT(VARCHAR(4), user_id) +'.'+ user_name as name from user_list
mysql 中
select CONCAT(user_id,'.',user_name) as name from user_list;