一、行转列
1.1、初始测试数据
表结构：TEST_TB_GRADE
Sql代码:
1 create table TEST_TB_GRADE
2 (
3 ID NUMBER(10) not null,
4 USER_NAME VARCHAR2(20 CHAR),
5 COURSE VARCHAR2(20 CHAR),
6 SCORE FLOAT
7 )
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：
Sql代码:
1 select t.user_name,
2 sum(decode(t.course, '语文', score,null)) as CHINESE,
3 sum(decode(t.course, '数学', score,null)) as MATH,
4 sum(decode(t.course, '英语', score,null)) as ENGLISH
5 from test_tb_grade t
6 group by t.user_name
7 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：
Sql代码:
01 select t2.SCORE_GP,
02 sum(decode(t2.course, '语文', COUNTNUM,null)) as CHINESE,
03 sum(decode(t2.course, '数学', COUNTNUM,null)) as MATH,
04 sum(decode(t2.course, '英语', COUNTNUM,null)) as ENGLISH
05 from (
06 select t.course,
07 case when t.score <60 then '00-60'
08 when t.score >=60 and t.score <80 then '60-80'
09 when t.score >=80 then '80-100' end as SCORE_GP,
10 count(t.score) as COUNTNUM
11 FROM test_tb_grade t
12 group by t.course,
13 case when t.score <60 then '00-60'
14 when t.score >=60 and t.score <80 then '60-80'
15 when t.score >=80 then '80-100' end
16 order by t.course ) t2
17 group by t2.SCORE_GP
18 order by t2.SCORE_GP
二、列转行
1.1、初始测试数据
表结构： TEST_TB_GRADE2
Sql代码:
1 create table TEST_TB_GRADE2
2 (
3 ID NUMBER(10) not null,
4 USER_NAME VARCHAR2(20 CHAR),
5 CN_SCORE FLOAT,
6 MATH_SCORE FLOAT,
7 EN_SCORE FLOAT
8 )
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：
Sql代码:
1 select user_name, 'CN_SCORE' COURSE , CN_SCORE as SCORE from test_tb_grade2
2 union
3 select user_name, 'MATH_SCORE' COURSE, MATH_SCORE as SCORE from test_tb_grade2
4 union
5 select user_name, 'EN_SCORE' COURSE, EN_SCORE as SCORE from test_tb_grade2
6 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：
Sql代码:
1 create table TEST_TB_GRADE3
2 (
3 USER_NAME VARCHAR2(20 CHAR),
4 COURSE VARCHAR2(20 CHAR),
5 SCORE FLOAT
6 )
再执行下面的sql：
Sql代码:
1 insert all
2 into test_tb_grade3(USER_NAME,COURSE,SCORE) values(user_name, '语文', CN_SCORE)
3 into test_tb_grade3(USER_NAME,COURSE,SCORE) values(user_name, '数学', MATH_SCORE)
4 into test_tb_grade3(USER_NAME,COURSE,SCORE) values(user_name, '英语', EN_SCORE)
5 select user_name, CN_SCORE, MATH_SCORE, EN_SCORE from test_tb_grade2;
6 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。
