oracle的列转行

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首先创建测试环境

create table test1(
user_account varchar2(100),
signup_date date,
user_email varchar2(100),
friend1_email varchar2(100),
friend2_email varchar2(100),
friend3_email varchar2(100)
);

insert into test1
values
  ('Rjbryla',
   to_date('2009-08-21', 'yyyy-mm-dd'),
   '[email protected]',
   '[email protected]',
   '[email protected]',
   '[email protected]');

insert into test1
values
  ('johndoe',
   to_date('2009-08-22', 'yyyy-mm-dd'),
   '[email protected]',
   null,
   '[email protected]',
   null);

--查询表中的内容

   select user_account, signup_date, src_col_name, friend_email
  from test1 unpivot((friend_email) for src_col_name in(user_email,
                                                               friend1_email,
                                                               friend2_email,
                                                               friend3_email));

该语句的作用就是将列转成行，src_col_name.friend_email是临时变量，unpivot（聚合函数 for 列名 in（类型）） 是基本语法  ，其中 in(‘’) 中可以指定别名，in中还可以指定子查询；该语句查询出来的结果如下图所示：

oracle11g之前的sql语句为：

select user_account,signup_date,'USER_EMAIL' as src_col_name,user_email as friend_email from test1
where user_email is not null
union
select user_account,signup_date,'FRIEND1_EMAIL' as src_col_name,user_email as friend_email from test1
where friend1_email is not null
union
select user_account,signup_date,'FRIEND2_EMAIL' as src_col_name,user_email as friend_email from test1
where friend2_email is not null
union
select user_account,signup_date,'FRIEND3_EMAIL' as src_col_name,user_email as friend_email from test1
where friend3_email is not null;