sql解惑之里程碑 谜题25（行转列）

create table servicesschedule
(
shop_id char(3) not null,
order_nbr char(10) not null,
sch_seq integer not null check(sch_seq in (1,2,3)),
service_type char(2) not null,
sch_date date,
primary key(shop_id,order_nbr,sch_seq)
)

insert into servicesschedule
select '002','4155526710',1,'01',date '1994-07-16' from dual union all
select '002','4155526710',2,'01',date '1994-07-30' from dual union all
select '002','4155526710',3,'01',date '1994-10-01' from dual union all
select '002','4155526711',1,'01',date '1994-07-16' from dual union all
select '002','4155526711',2,'01',date '1994-07-30' from dual union all
select '002','4155526711',3,'01',null from dual;

select order_nbr, "1" as proc, "2" as com, "3" as con
from (select order_nbr, sch_seq, sch_date from servicesschedule)
/**/ pivot(max(sch_date) for sch_seq in(1, 2, 3))