我有id，cost和priority列的表：
create table a_test_table (id number(4,0), cost number(15,2), priority number(4,0));
insert into a_test_table (id, cost, priority) values (1, 1000000, 10);
insert into a_test_table (id, cost, priority) values (2, 10000000, 9);
insert into a_test_table (id, cost, priority) values (3, 5000000, 8);
insert into a_test_table (id, cost, priority) values (4, 19000000, 7);
insert into a_test_table (id, cost, priority) values (5, 20000000, 6);
insert into a_test_table (id, cost, priority) values (6, 15000000, 5);
insert into a_test_table (id, cost, priority) values (7, 2000000, 4);
insert into a_test_table (id, cost, priority) values (8, 3000000, 3);
insert into a_test_table (id, cost, priority) values (9, 3000000, 2);
insert into a_test_table (id, cost, priority) values (10, 8000000, 1);
commit;
select
id,
to_char(cost, '$999,999,999') as cost,
priority
from
a_test_table;
ID COST PRIORITY ---------- ------------- ---------- 1 $1,000,000 10 2 $10,000,000 9 3 $5,000,000 8 4 $19,000,000 7 5 $20,000,000 6 6 $15,000,000 5 7 $2,000,000 4 8 $3,000,000 3 9 $3,000,000 2 10 $8,000,000 1
从最高优先级（降序）开始，我想选择cost加起来小于（或等于）$ 20,000,000的行。
结果如下所示：
ID COST PRIORITY
---------- ------------- ----------
1 $1,000,000 10
2 $10,000,000 9
3 $5,000,000 8
7 $2,000,000 4
Total: $18,000,000
如何使用Oracle SQL执行此操作？
这是一种在纯SQL中执行此操作的方法。我不会发誓没有更好的方法。
基本上，它使用递归公用表表达式（即WITH costed...）来计算总计小于20,000,000的每个可能的元素组合。
然后它从该结果获得第一个完整路径。
然后，它获取该路径中的所有行。
注意：逻辑假设没有id超过5位数。那是LPAD(id,5,'0')的东西。
WITH costed (id, cost, priority, running_cost, path) as
( SELECT id, cost, priority, cost running_cost, lpad(id,5,'0') path
FROM a_test_table
WHERE cost <= 20000000
UNION ALL
SELECT a.id, a.cost, a.priority, a.cost + costed.running_Cost, costed.path || '|' || lpad(a.id,5,'0')
FROM costed, a_test_table a
WHERE a.priority < costed.priority
AND a.cost + costed.running_cost <= 20000000),
best_path as (
SELECT *
FROM costed c
where not exists ( SELECT 'longer path' FROM costed c2 WHERE c2.path like c.path || '|%' )
order by path
fetch first 1 row only )
SELECT att.*
FROM best_path cross join a_test_table att
WHERE best_path.path like '%' || lpad(att.id,5,'0') || '%'
order by att.priority desc;
+----+----------+----------+ | ID | COST | PRIORITY | +----+----------+----------+ | 1 | 1000000 | 10 | | 2 | 10000000 | 9 | | 3 | 5000000 | 8 | | 7 | 2000000 | 4 | +----+----------+----------+
此版本使用MATCH_RECOGNIZE查找递归CTE后最佳组中的所有行：
WITH costed (id, cost, priority, running_cost, path) as
( SELECT id, cost, priority, cost running_cost, lpad(id,5,'0') path
FROM a_test_table
WHERE cost <= 20000000
UNION ALL
SELECT a.id, a.cost, a.priority, a.cost + costed.running_Cost, costed.path || '|' || lpad(a.id,5,'0')
FROM costed, a_test_table a
WHERE a.priority < costed.priority
AND a.cost + costed.running_cost <= 20000000)
search depth first by priority desc set ord
SELECT id, cost, priority
FROM costed c
MATCH_RECOGNIZE (
ORDER BY path
MEASURES
MATCH_NUMBER() AS mno
ALL ROWS PER MATCH
PATTERN (STRT ADDON*)
DEFINE
ADDON AS ADDON.PATH = PREV(ADDON.PATH) || '|' || LPAD(ADDON.ID,5,'0')
)
WHERE mno = 1
ORDER BY priority DESC;
*编辑：在递归CTE的锚点部分中删除了ROWNUM=1的使用，因为它依赖于将返回行的任意顺序。我很惊讶没有人对此感到愤怒。 *
WITH costed (id, cost, priority, running_cost) as
( SELECT id, cost, priority, cost running_cost
FROM ( SELECT * FROM a_test_table
WHERE cost <= 20000000
ORDER BY priority desc
FETCH FIRST 1 ROW ONLY )
UNION ALL
SELECT a.id, a.cost, a.priority, a.cost + costed.running_Cost
FROM costed CROSS APPLY ( SELECT b.*
FROM a_test_table b
WHERE b.priority < costed.priority
AND b.cost + costed.running_cost <= 20000000
FETCH FIRST 1 ROW ONLY
) a
)
CYCLE id SET is_cycle TO 'Y' DEFAULT 'N'
select id, cost, priority from costed
order by priority desc
在普通的SQL中，我太愚蠢了，所以我尝试了PL / SQL - 一个返回表的函数。这是如何：循环遍历表中的所有行，我正在计算总和;如果它低于限制，那么很好 - 将行的ID添加到数组中并继续。
SQL> create or replace function f_pri (par_limit in number)
2 return sys.odcinumberlist
3 is
4 l_sum number := 0;
5 l_arr sys.odcinumberlist := sys.odcinumberlist();
6 begin
7 for cur_r in (select id, cost, priority
8 from a_test_table
9 order by priority desc
10 )
11 loop
12 l_sum := l_sum + cur_r.cost;
13 if l_sum <= par_limit then
14 l_arr.extend;
15 l_arr(l_arr.last) := cur_r.id;
16 else
17 l_sum := l_sum - cur_r.cost;
18 end if;
19 end loop;
20 return (l_arr);
21 end;
22 /
Function created.
准备SQL * Plus环境以使输出看起来更漂亮：
SQL> break on report
SQL> compute sum of cost on report
SQL> set ver off
测试：
SQL> select t.id, t.cost, t.priority
2 from table(f_pri(&par_limit)) x join a_test_table t on t.id = x.column_value
3 order by t.priority desc;
Enter value for par_limit: 20000000
ID COST PRIORITY
---------- ---------- ----------
1 1000000 10
2 10000000 9
3 5000000 8
7 2000000 4
----------
sum 18000000
SQL> /
Enter value for par_limit: 30000000
ID COST PRIORITY
---------- ---------- ----------
1 1000000 10
2 10000000 9
3 5000000 8
7 2000000 4
8 3000000 3
9 3000000 2
----------
sum 24000000
6 rows selected.
SQL>