select 11 from dualunion select 11 from dual

select 11 from dualunion allselect 11 from dual

2.1 select t.*, t.rowid from users t order by 1,2
--按照列号排序

2.2 select t.*, t.rowid from users t order by t.name nulls first
-- 该字段空值排前面
select t.*, t.rowid from users t order by t.name nulls last
-- 该字段空值排后面

2.3 select t.*, t.rowid from users t where t.name in（‘admin‘,‘test2‘,‘测试‘）order by instr(‘admin,test2,测试‘,t.name)
--按in顺序排序

2.3.1 select t.*, t.rowid from users t order by instr(‘admin,test2,测试‘,t.name) desc 
--按in顺序排序 ps：排在最底部 各位可以按需求对 instr里面的值进行调整

select utl_raw.cast_to_varchar2(utl_encode.base64_decode(utl_raw.cast_to_raw(‘MTEuMg==‘))) as "Base64解码后数据" from dual --解密 结果11.2

select utl_raw.cast_to_varchar2(utl_encode.base64_encode(utl_raw.cast_to_raw(11.2))) from dual -- 加密 结果 MTEuMg==

 select t.rnum  from (SELECT rownum rnum FROM ALL_OBJECTS WHERE ROWNUM <= 10 ) t where mod(t.rnum,3)=0 ; --10以内被3整除的数 结果 3,6,9 select sum(t.rnum) as total_sum from (SELECT rownum rnum FROM ALL_OBJECTS WHERE ROWNUM <= 10 ) t where mod(t.rnum,3)=0 ; --10以内被3整除的数的和 结果 18

select decode（AA,‘11‘,‘数据是11‘,‘22‘,‘数据是22‘,‘其他数据‘) as "数据结果"from(select 11 as AA from dualunion allselect 22 from dualunion allselect 221 from dualunion allselect 333 from dual)

select t.* from sys_tree t where t.isdel=1start with t.code=‘100‘connect by prior t.id = t.pidorder by t.orderno--查询所有的子节点                        select t.* from sys_tree t where t.isdel=1start with t.code=‘100‘connect by prior t.pid = t.idorder by t.orderno--查询所有的父节点