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
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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：
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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：
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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
2.1、初始测试数据
表结构：TEST_TB_GRADE2
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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：
2.2、 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：
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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：
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create table TEST_TB_GRADE3 ( USER_NAME VARCHAR2(20 CHAR), COURSE VARCHAR2(20 CHAR), SCORE FLOAT ) |
再执行下面的sql：
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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。
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