oracle 数据库开发面试题，当时笔试的时候一个没做出来，现附原题及答案

--创建表及数据
CREATE TABLE tt(ID INTEGER);

INSERT INTO tt 
SELECT 1 FROM dual
UNION ALL
SELECT 2 FROM dual
UNION ALL
SELECT 3 FROM dual
UNION ALL
SELECT 5 FROM dual
UNION ALL
SELECT 6 FROM dual
UNION ALL
SELECT 7 FROM dual
UNION ALL
SELECT 8 FROM dual
UNION ALL
SELECT 10 FROM dual
UNION ALL
SELECT 11 FROM dual
UNION ALL
SELECT 12 FROM dual
UNION ALL
SELECT 15 FROM dual;
COMMIT;

--用到了connect by level 造数据
WITH IT AS
 (SELECT LEVEL ID FROM DUAL CONNECT BY LEVEL <= (SELECT MAX(ID) FROM TT))
SELECT A.ID
  FROM IT A
 WHERE NOT EXISTS (SELECT 1 FROM TT B WHERE A.ID = B.ID)

--单行单列转多行
--创建表及数据
create table ttt(id integer,room varchar2(200));

insert into ttt
select 1,‘101,102‘ from dual
union all
select 2,‘201,202,203‘ from dual
union all
select 3,‘301‘ from dual;
commit;

SELECT DISTINCT ID,REGEXP_SUBSTR(room, ‘[^,]+‘, 1, LEVEL, ‘i‘) AS STR  
  FROM ttt
CONNECT BY LEVEL <= LENGTH(room) - LENGTH(REGEXP_REPLACE(room, ‘,‘, ‘‘))+1;