请教各位神侠,我想实现一个自定义函数,函数类型为 f_max(列名 column_name, 序号 val),要求此函数实现 求得列名为 column_name 的这个列的第 val个最大的值。比如有一个表如下 CREATE TABLE t (id VARCHAR2(2), n INT);
INSERT INTO t VALUES ('A',25);
INSERT INTO t VALUES ('A',30);
INSERT INTO t VALUES ('A',55);
INSERT INTO t VALUES ('B',77);
INSERT INTO t VALUES ('C',7176);
INSERT INTO t VALUES ('C',5428);
INSERT INTO t VALUES ('C',7820);要求select f_max(n,1) from t 的结果为 7820, 对应为最大的 n,
select f_max(n,2) from t 的结果为 7176, 对应为第二个最大的 n,...如能帮助,万分感谢!!!
INSERT INTO t VALUES ('A',25);
INSERT INTO t VALUES ('A',30);
INSERT INTO t VALUES ('A',55);
INSERT INTO t VALUES ('B',77);
INSERT INTO t VALUES ('C',7176);
INSERT INTO t VALUES ('C',5428);
INSERT INTO t VALUES ('C',7820);要求select f_max(n,1) from t 的结果为 7820, 对应为最大的 n,
select f_max(n,2) from t 的结果为 7176, 对应为第二个最大的 n,...如能帮助,万分感谢!!!
--不用自己定义吧!
--sql1: SELECT N,row_number() over(ORDER BY n DESC) rn FROM t--result:
7820 1
7176 2
5428 3
77 4
55 5
30 6
25 7--sql2 SELECT N
FROM
( SELECT N,row_number() over(ORDER BY n DESC) rn FROM t)
WHERE rn=1--result
7820
SELECT N
FROM
( SELECT N,row_number() over(ORDER BY n DESC) rn FROM t)
WHERE rn=2--result:
7176
(
max NUMBER, -- highest value seen so far
secmax NUMBER, -- second highest value seen so far
static function ODCIAggregateInitialize(sctx IN OUT SecondMaxImpl)
return number,
member function ODCIAggregateIterate(self IN OUT SecondMaxImpl,
value IN number) return number,
member function ODCIAggregateTerminate(self IN SecondMaxImpl,
returnValue OUT number, flags IN number) return number,
member function ODCIAggregateMerge(self IN OUT SecondMaxImpl,
ctx2 IN SecondMaxImpl) return number
);
/ Implement the type body for SecondMaxImpl. create or replace type body SecondMaxImpl is
static function ODCIAggregateInitialize(sctx IN OUT SecondMaxImpl)
return number is
begin
sctx := SecondMaxImpl(0, 0);
return ODCIConst.Success;
end; member function ODCIAggregateIterate(self IN OUT SecondMaxImpl, value IN number)
return number is
begin
if value > self.max then
self.secmax := self.max;
self.max := value;
elsif value > self.secmax then
self.secmax := value;
end if;
return ODCIConst.Success;
end; member function ODCIAggregateTerminate(self IN SecondMaxImpl, returnValue OUT
number, flags IN number) return number is
begin
returnValue := self.secmax;
return ODCIConst.Success;
end; member function ODCIAggregateMerge(self IN OUT SecondMaxImpl, ctx2 IN
SecondMaxImpl) return number is
begin
if ctx2.max > self.max then
if ctx2.secmax > self.secmax then
self.secmax := ctx2.secmax;
else
self.secmax := self.max;
end if;
self.max := ctx2.max;
elsif ctx2.max > self.secmax then
self.secmax := ctx2.max;
end if;
return ODCIConst.Success;
end;
end;
/ Create the user-defined aggregate. CREATE FUNCTION SecondMax (input NUMBER) RETURN NUMBER
PARALLEL_ENABLE AGGREGATE USING SecondMaxImpl;Using SecondMax()SELECT SecondMax(salary), department_id
FROM employees
GROUP BY department_id
HAVING SecondMax(salary) > 9000;
万分感谢!