數據人員Sql必會列轉行

列轉行上一篇博客已經介紹過了。

下面介紹一下行轉列的實現

假設咱們有一個數據表：

CREATE TABLE row_to_line
(
  user_name character varying(30) NOT NULL, -- 學生名稱
  yingyu integer, -- 得分
  yuwen integer,
  huaxue integer,
  wuli integer,  
  CONSTRAINT row_to_line_pkey PRIMARY KEY (user_name)
);

insert into row_to_line select 'liqiu', 80, 90, 90, 89;
insert into row_to_line select 'lingling', 89, 99, 100, 90;
insert into row_to_line select 'xingxing', 90, 94, 97, 99;

顯示以下：

那麼咱們想要將它轉化爲一列列的以下結果輸出：

那麼如何作到哪？

方法1、簡單可讀性強：

select
  a.user_name,
  a.title,
  a.score
from 
(
  (select user_name, yingyu as "score", 'yingyu' as title from row_to_line)
  union (select user_name, yuwen as "score", 'yuwen' as title from row_to_line)
  union (select user_name, huaxue as "score", 'huaxue' as title from row_to_line)
  union (select user_name, wuli as "score", 'wuli' as title from row_to_line)
) a
order by a.user_name, a.title

方法2、快速

這是pg的專有方法

select * from tmp.dim_values_20170821 limit 10

 

 select lower(regexp_split_to_table(dim_values, ' ')) as dim_name, table_name,all_num from tmp.dim_values_20170821 where table_name = '景區統計表'