--case when 的行转列
select e.job  as "工作"，
case e.deptno when 10 then sal end as " 部门 10 工资",
case e.deptno when 20 then sal end as "部门 20 工资",
case e.deptno when 30 then sal end as "部门 30 工资",
e.sal as "合计工资"
from emp e  order by 1

--通过工作岗位分组
select e.job as "工作"， sum(case e.deptno
           when 10 then
            sal
       end) as " 部门 10 工资",
       sum(case e.deptno
                when 20 then
                 sal
            end) as "部门 20 工资",
       sum(case e.deptno
                when 30 then
                 sal
            end) as "部门 30 工资", sum(e.sal) as "合计工资"
  from emp e
 group by job
 order by 1

--PVIOT
select *
  from (select job, sal, deptno from emp)
pivot(sum(sal) as sal
   for deptno in(10 as d10, 20 as d20, 30 as d30))
 order by 1
--PIVOT只能按一个条件来完成"行转列”，如果同时把工作与部门都转为列，加以汇总时，PIVOT就无能为力了，
--只能用case when
select count(case
                 when deptno = 10 then
                  ename
             end) as deptno_10,
       count(case
                 when deptno = 20 then
                  ename
             end) as deptno_20,
       count(case
                 when deptno = 30 then
                  ename
             end) as deptno_30,
       count(case
                 when job = 'CLERK' then
                  ename
             end) as clerks,
       count(case
                 when job = 'MANAGER' then
                  ename
             end) as MANAGER,
       count(case
                 when job = 'PRESIDENT' then
                  ename
             end) as PRESIDENT,
       count(case
                 when job = 'ANALYST' then
                  ename
             end) as ANALYST,
       count(case
                 when job = 'SALESMAN' then
                  ename
             end) as SALESMAN
  from emp
 --列转行
 create table test as
select *
  from (select deptno, sal from emp)
pivot(count(1) as cnt, sum(sal) as sal
   for deptno in(10 as deptno_10, 20 as deptno_20, 30 as deptno_30))
 order by 1
--需求把3个部门的人次显示为一列,比较笨写法。
select '10' as "部门编码", deptno_10_cnt as "人次"
  from test
union all
select '20' as "部门编码", deptno_20_cnt as "人次"
  from test
union all
select '30' as "部门编码", deptno_30_cnt as "人次"
  from test
--用unpivot
select deptno as 列名, substr(deptno, -6, 2) as 部门编码，人次
  from test unpivot(人次 for deptno in(deptno_10_cnt,
                                      deptno_20_cnt,
                                      deptno_30_cnt))
--如果要把人次和工资同时转换，得用连接
select a.列名, a.部门编码, a.人次, b.工资
  from (select substr(deptno, 1, 9) as 列名, substr(deptno, -6, 2) as 部门编码，人次
           from test unpivot include nulls(人次 for deptno in(deptno_10_cnt,
                                                             deptno_20_cnt,
                                                             deptno_30_cnt))) a

 inner join (select substr(deptno, 1, 9) as 列名，工资
               from test unpivot include nulls(工资 for deptno in(deptno_10_sal,
                                                                 deptno_20_sal,
                                                                 deptno_30_sal))) b
    on (a.列名 = b.列名)
--不用join 还是用unpivot
select deptno as 部门编码, 工资, 人次
  from test unpivot include nulls(人次 for deptno in(deptno_10_cnt as 10,
                                                    deptno_20_cnt as 20,
                                                    deptno_30_cnt as 30)) unpivot include nulls(工资 for deptno2 in(deptno_10_sal as 10,
                                                                                                                  deptno_20_sal as 20,
                                                                                                                  deptno_30_sal as 30))
 where deptno = deptno2
 
--抑制结果集中的重复值
select case
           when lag(e.job) over(order by job, ename) = job then
            null
           else
            job
       end as 职位, ename as 姓名
  from emp e
 where e.deptno = 20
 order by e.job, e.ename