oracle A點出發到各地的路徑及其距離

求所有的可能路徑及距離,樣例數據如下：

with bus as
(
select 1 id, 'A' dstart, 'B' dend, '120' distance from dual union all
select 2 id, 'B' dstart, 'C' dend, '200' distance from dual union all
select 3 id, 'C' dstart, 'E' dend, '180' distance from dual union all
select 4 id, 'A' dstart, 'D' dend, '150' distance from dual union all
select 5 id, 'D' dstart, 'M' dend, '300' distance from dual union all
select 6 id, 'F' dstart, 'M' dend, '260' distance from dual
)
select * From bus;

實現效果:

SUM_DISTANCE	PATH
120		A->B
320		A->B->C
500		A->B->C->E
150		A->D
450		A->D->M
200		B->C
380		B->C->E
180		C->E
300		D->M
260		F->M

原始SQL代碼：

with bus as
(
select 1 id, 'A' dstart, 'B' dend, '120' distance from dual union all
select 2 id, 'B' dstart, 'C' dend, '200' distance from dual union all
select 3 id, 'C' dstart, 'E' dend, '180' distance from dual union all
select 4 id, 'A' dstart, 'D' dend, '150' distance from dual union all
select 5 id, 'D' dstart, 'M' dend, '300' distance from dual union all
select 6 id, 'F' dstart, 'M' dend, '260' distance from dual 
)
select level, a.dstart, a.dend, 
       sys_connect_by_path(distance,'+')  sum_distance,
       (select sum(b.distance) from bus b start with b.id=a.id connect by prior dstart =  dend
       ),
       CONNECT_BY_root(a.dstart)|| sys_connect_by_path(a.dend,'->')  path,
       CONNECT_BY_ISLEAF leaf      
from bus a
connect by prior dend =  dstart;

一看這個SQL語句裏有一個標量子查詢，數據量少的時候看不出來問題，多的時候就會出現性能問題，因此利用dbms_aw.eval_number函數處理了樹形函數的返回值,優化後的SQL代碼 ：

with bus as
(
select 1 id, 'A' dstart, 'B' dend, '120' distance from dual union all
select 2 id, 'B' dstart, 'C' dend, '200' distance from dual union all
select 3 id, 'C' dstart, 'E' dend, '180' distance from dual union all
select 4 id, 'A' dstart, 'D' dend, '150' distance from dual union all
select 5 id, 'D' dstart, 'M' dend, '300' distance from dual union all
select 6 id, 'F' dstart, 'M' dend, '260' distance from dual 
)
select level, a.dstart, a.dend, ltrim(sys_connect_by_path(distance,'+'),'+') distance_expression,
       dbms_aw.eval_number(ltrim(sys_connect_by_path(distance,'+'),'+'))  sum_distance,
       CONNECT_BY_root(a.dstart)|| sys_connect_by_path(a.dend,'->')  path,
       CONNECT_BY_ISLEAF leaf      
from bus a
connect by prior dend =  dstart;

參考:http://blog.csdn.net/jgmydsai/article/details/38985577