sql技巧（五）行转列和列转行

参考链接

行转列容易理解：依次查询所需要的列用union连接

列转化行这个用sum(case  when  then ) 或者max(case when then  ） 结构选取特定行的数据作为列数据！

列转化为行

数据表

结果表

SELECT  user_name ,

MAX(CASE course  WHEN'数学'  THEN  score   ELSE 0 END) 数学,

MAX(CASEcourseWHEN'语文'THENscoreELSE0END) 语文,

MAX(CASEcourseWHEN'英语'THENscoreELSE0END) 英语

FROMtest_tb_grade

GROUP   BY   USER_NAME;

行转化为列

数据表

结果表

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;