How to find all associated child records through a parent record in SQL Server

4 levels of SQL code can be found

Select menu_id,menu_name,father_id from Sys_menu where menu_id= ' or father_id=18 or--first level, level two father_id in  
(select M  enu_id from Sys_menu a where  menu_id= ' or father_id=18 ' or   --level three father_id in  
(select menu_id from Sys_menu where father_id in (select menu_id from Sys_menu a where  menu_id= ' or father_id=18))--level four

Select menu_id,menu_name,father_id from Sys_menu where menu_id= ' or father_id=18 or--first level, level two

father_id in (select menu_id from Sys_menu a where menu_id= ' or father_id=18) or--level three

father_id in (select menu_id to Sys_menu where father_id in (select menu_id from Sys_menu a where menu_id= ' or fathe R_ID=18))--level four

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