计算层次结构路径的顶层？答案

【问题标题】：Calculate top-level of hierarchy path?计算层次结构路径的顶层？
【发布时间】：2020-04-01 19:26:05
【问题描述】：

我有一个classstructure 表：

create table classstructure (classstructureid number(8,0), classificationid varchar2(25), parent number(8,0));

insert into classstructure(classstructureid, classificationid, parent) values(1001, 'FLEET', null);
insert into classstructure(classstructureid, classificationid, parent) values(1002, 'LIGHTDUTYVEHICLE', 1001);
insert into classstructure(classstructureid, classificationid, parent) values(1004, 'MEDIUMDUTYVEHICLE', 1001);
insert into classstructure(classstructureid, classificationid, parent) values(1022, 'ACTIVETRANSPORTATION', null);
insert into classstructure(classstructureid, classificationid, parent) values(1023, 'FACILITYWALKWAY', 1022);
insert into classstructure(classstructureid, classificationid, parent) values(1024, 'TRAIL', 1022);
insert into classstructure(classstructureid, classificationid, parent) values(1085, 'SIDEWALK', 1022);
insert into classstructure(classstructureid, classificationid, parent) values(1091, 'SDWRAMP', 1085);
commit;

select * from classstructure;

CLASSSTRUCTUREID CLASSIFICATIONID              PARENT
---------------- ------------------------- ----------
            1001 FLEET                               
            1002 LIGHTDUTYVEHICLE                1001
            1004 MEDIUMDUTYVEHICLE               1001

            1022 ACTIVETRANSPORTATION                
            1023 FACILITYWALKWAY                 1022
            1024 TRAIL                           1022
            1085 SIDEWALK                        1022
            1091 SDWRAMP                         1085

我想计算每一行的层次路径的顶层：

CLASSSTRUCTUREID TOP LEVEL
---------------- ---------
1001             FLEET
1002             FLEET
1004             FLEET

1022             ACTIVETRANSPORTATION
1023             ACTIVETRANSPORTATION
1024             ACTIVETRANSPORTATION
1085             ACTIVETRANSPORTATION
1091             ACTIVETRANSPORTATION

是否可以使用 Oracle 18c SQL 做到这一点？

【问题讨论】：

标签： sql oracle parent-child hierarchical-data maximo

【解决方案1】：

您可以使用hierarchical query 和connect_by_root：

select classstructureid, connect_by_root(classificationid)
from classstructure
connect by parent = prior classstructureid
start with parent is null;

db<>fiddle

【讨论】：