oracle，sqlserver,mysql 栏位合并sql

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;