数据库 行转列 列转行详解

目录结构如下：

• 行转列
• 列转行

[一]、行转列

 

1.1、初始测试数据

 

表结构：TEST_TB_GRADE

 

(
  ID        NUMBER(10) not null,
  USER_NAME VARCHAR2(20 CHAR),
  COURSE    VARCHAR2(20 CHAR),
  SCORE     FLOAT
)

create table TEST_TB_GRADE
(
  ID        NUMBER(10) not null,
  USER_NAME VARCHAR2(20 CHAR),
  COURSE    VARCHAR2(20 CHAR),
  SCORE     FLOAT
)

 初始数据如下图：

                        

 

1.2、 如果需要实现如下的查询效果图：

                     

 

这就是最常见的行转列，主要原理是利用decode函数、聚集函数(sum)，结合group by分组实现的，具体的sql如下：

  sum(decode(t.course, '语文', score,null)) as CHINESE,
  sum(decode(t.course, '数学', score,null)) as MATH,
  sum(decode(t.course, '英语', score,null)) as ENGLISH
from test_tb_grade t
group by t.user_name
order by t.user_name

select t.user_name,
  sum(decode(t.course, '语文', score,null)) as CHINESE,
  sum(decode(t.course, '数学', score,null)) as MATH,
  sum(decode(t.course, '英语', score,null)) as ENGLISH
from test_tb_grade t
group by t.user_name
order by t.user_name

 

 

1.3、延伸

 

如果要实现对各门功课的不同分数段进行统计，效果图如下：

                 

 

具体的实现sql如下：

  sum(decode(t2.course, '语文', COUNTNUM,null)) as CHINESE,
  sum(decode(t2.course, '数学', COUNTNUM,null)) as MATH,
  sum(decode(t2.course, '英语', COUNTNUM,null)) as ENGLISH
from (
  select t.course,
         case when t.score  <60 then '00-60'
              when t.score >=60 and t.score <80  then '60-80'
              when t.score >=80 then '80-100' end as SCORE_GP,
         count(t.score) as COUNTNUM
  FROM test_tb_grade t
  group by t.course,
        case when t.score  <60  then '00-60'
              when t.score >=60 and t.score <80  then '60-80'
              when t.score >=80 then '80-100' end
  order by t.course ) t2
group by t2.SCORE_GP
order by t2.SCORE_GP

select t2.SCORE_GP,
  sum(decode(t2.course, '语文', COUNTNUM,null)) as CHINESE,
  sum(decode(t2.course, '数学', COUNTNUM,null)) as MATH,
  sum(decode(t2.course, '英语', COUNTNUM,null)) as ENGLISH
from (
  select t.course,
         case when t.score  <60 then '00-60'
              when t.score >=60 and t.score <80  then '60-80'
              when t.score >=80 then '80-100' end as SCORE_GP,
         count(t.score) as COUNTNUM
  FROM test_tb_grade t
  group by t.course,
        case when t.score  <60  then '00-60'
              when t.score >=60 and t.score <80  then '60-80'
              when t.score >=80 then '80-100' end
  order by t.course ) t2
group by t2.SCORE_GP
order by t2.SCORE_GP

 

[二]、列转行

 

1.1、初始测试数据

        表结构：TEST_TB_GRADE2

(
  ID         NUMBER(10) not null,
  USER_NAME  VARCHAR2(20 CHAR),
  CN_SCORE   FLOAT,
  MATH_SCORE FLOAT,
  EN_SCORE   FLOAT
)

create table TEST_TB_GRADE2
(
  ID         NUMBER(10) not null,
  USER_NAME  VARCHAR2(20 CHAR),
  CN_SCORE   FLOAT,
  MATH_SCORE FLOAT,
  EN_SCORE   FLOAT
)

 

        初始数据如下图：

        

 

1.2、 如果需要实现如下的查询效果图：

                       

 

这就是最常见的列转行，主要原理是利用SQL里面的union，具体的sql语句如下：

union select user_name, '数学' COURSE, MATH_SCORE as SCORE from test_tb_grade2
union select user_name, '英语' COURSE, EN_SCORE as SCORE from test_tb_grade2
order by user_name,COURSE

select user_name, '语文' COURSE , CN_SCORE as SCORE from test_tb_grade2
union select user_name, '数学' COURSE, MATH_SCORE as SCORE from test_tb_grade2
union select user_name, '英语' COURSE, EN_SCORE as SCORE from test_tb_grade2
order by user_name,COURSE

 

 也可以利用【 insert all into ... select 】来实现，首先需要先建一个表TEST_TB_GRADE3：

    (
      USER_NAME VARCHAR2(20 CHAR),
      COURSE    VARCHAR2(20 CHAR),
      SCORE     FLOAT
    )

create table TEST_TB_GRADE3
    (
      USER_NAME VARCHAR2(20 CHAR),
      COURSE    VARCHAR2(20 CHAR),
      SCORE     FLOAT
    )

 再执行下面的sql：

 

into test_tb_grade3(USER_NAME,COURSE,SCORE) values(user_name, '语文', CN_SCORE)
into test_tb_grade3(USER_NAME,COURSE,SCORE) values(user_name, '数学', MATH_SCORE)
into test_tb_grade3(USER_NAME,COURSE,SCORE) values(user_name, '英语', EN_SCORE)
select user_name, CN_SCORE, MATH_SCORE, EN_SCORE from test_tb_grade2;
commit;

insert all
into test_tb_grade3(USER_NAME,COURSE,SCORE) values(user_name, '语文', CN_SCORE)
into test_tb_grade3(USER_NAME,COURSE,SCORE) values(user_name, '数学', MATH_SCORE)
into test_tb_grade3(USER_NAME,COURSE,SCORE) values(user_name, '英语', EN_SCORE)
select user_name, CN_SCORE, MATH_SCORE, EN_SCORE from test_tb_grade2;
commit;

 别忘记commit操作，然后再查询TEST_TB_GRADE3，发现表中的数据就是列转成行了。

 

 

本文连接：http://sjsky.iteye.com/blog/1152167

来源： <http://blog.csdn.net/mezheng/article/details/7426765>

 

来自为知笔记(Wiz)