自定义Oracle聚集函数：模拟SUM,MAX,AVG

实现三个函数，关键都在于处理ODCIAggregateIterate()，即下面几张图中的高亮部分。Oracle自定义聚集函数的功能很强大，笔者暂时只钻研到这一层。
f_sum()，模拟SUM()函数：
定义TYPE：

create or replace type f_sum_type2 as object ( num number, static function ODCIAggregateInitialize(sctx In Out f_sum_type2) return number, member function ODCIAggregateIterate(self In Out f_sum_type2, value In number) return number, member function ODCIAggregateMerge(self In Out f_sum_type2, ctx2 In f_sum_type2) return number, member function ODCIAggregateTerminate(self In Out f_sum_type2, returnValue Out number, flags In number) return number )

定义TYPE BODY：

create or replace type body f_sum_type2 is static function ODCIAggregateInitialize (sctx In Out f_sum_type2) return number is begin sctx := f_sum_type2(0); return ODCIConst.Success; end; member function ODCIAggregateIterate (self In Out f_sum_type2, value In number) return number is begin self.num := self.num + value; return ODCIConst.Success; end; member function ODCIAggregateMerge(self In Out f_sum_type2, ctx2 In f_sum_type2) return number is BEGIN self.num := self.num; return ODCIconst.Success; end; member function ODCIAggregateTerminate(self In Out f_sum_type2, returnValue Out number, flags In number) return number is begin returnValue := self.num; return ODCIConst.Success; end; end;

定义函数：

CREATE OR REPLACE FUNCTION f_sum2(input number ) RETURN number PARALLEL_ENABLE AGGREGATE USING f_sum_type2;

测试：

SQL> select f_sum2(id),sum(id) from "tblabc" 2 ; F_SUM2(ID) SUM(ID) ---------- ---------- 5247 5247 SQL>

f_max()，模拟MAX()函数：
定义TYPE：

CREATE OR REPLACE TYPE f_max_type AS OBJECT ( var NUMBER, STATIC FUNCTION ODCIAggregateInitialize(sctx IN OUT f_max_type) RETURN NUMBER, MEMBER FUNCTION ODCIAggregateIterate(SELF IN OUT f_max_type, VALUE IN NUMBER) RETURN NUMBER, MEMBER FUNCTION ODCIAggregateMerge(SELF IN OUT f_max_type, ctx2 IN OUT f_max_type) RETURN NUMBER, MEMBER FUNCTION ODCIAggregateTerminate(SELF IN OUT f_max_type, returnValue OUT NUMBER, flags IN NUMBER) RETURN NUMBER )

定义TYPE BODY：

CREATE OR REPLACE TYPE BODY f_max_type IS STATIC FUNCTION ODCIAggregateInitialize(sctx IN OUT f_max_type) RETURN NUMBER IS BEGIN sctx := f_max_type(0); RETURN ODCIConst.Success; END; MEMBER FUNCTION ODCIAggregateIterate(SELF IN OUT f_max_type, VALUE IN NUMBER) RETURN NUMBER IS BEGIN IF SELF.var < VALUE THEN SELF.var := VALUE; END IF; RETURN ODCIConst.Success; END; MEMBER FUNCTION ODCIAggregateMerge(SELF IN OUT f_max_type, ctx2 IN OUT f_max_type) RETURN NUMBER IS BEGIN RETURN ODCIConst.Success; END; MEMBER FUNCTION ODCIAggregateTerminate(SELF IN OUT f_max_type, returnValue OUT NUMBER, flags IN NUMBER) RETURN NUMBER IS BEGIN returnValue := SELF.var; RETURN ODCIconst.success; END; END;

CREATE OR REPLACE FUNCTION f_max (input NUMBER) RETURN NUMBER PARALLEL_ENABLE AGGREGATE USING f_max_type;

SQL> select f_max(id),max(id) from "tblabc" 2 ; F_MAX(ID) MAX(ID) ---------- ---------- 303 303 SQL>

f_avg()，模拟AVG()函数：
定义TYPE：

CREATE OR REPLACE TYPE f_avg_type AS OBJECT ( SUM NUMBER, num NUMBER, STATIC FUNCTION ODCIAggregateInitialize(sctx IN OUT f_avg_type) RETURN NUMBER, MEMBER FUNCTION ODCIAggregateIterate(SELF IN OUT f_avg_type, VALUE IN NUMBER) RETURN NUMBER, MEMBER FUNCTION ODCIAggregateMerge(SELF IN OUT f_avg_type, ctx2 IN f_avg_type) RETURN NUMBER, MEMBER FUNCTION ODCIAggregateTerminate(SELF IN OUT f_avg_type, returnValue OUT NUMBER, flags IN NUMBER) RETURN NUMBER )

定义TYPE BODY：

CREATE OR REPLACE TYPE BODY f_avg_type IS STATIC FUNCTION ODCIAggregateInitialize(sctx IN OUT f_avg_type) RETURN NUMBER IS BEGIN sctx := f_avg_type(0, 0); RETURN ODCICONST.Success; END; MEMBER FUNCTION ODCIAggregateIterate (SELF IN OUT f_avg_type, VALUE IN NUMBER) RETURN NUMBER IS BEGIN SELF.SUM := SELF.SUM + VALUE; SELF.num := SELF.num + 1; RETURN ODCIConst.Success; END; MEMBER FUNCTION ODCIaggregateMerge(SELF IN OUT f_avg_type, ctx2 IN f_avg_type) RETURN NUMBER IS BEGIN RETURN ODCIConst.Success; END; MEMBER FUNCTION ODCIAggregateTerminate(SELF IN OUT f_avg_type, returnValue OUT NUMBER, flags IN NUMBER) RETURN NUMBER IS BEGIN returnValue := SELF.SUM/SELF.num; RETURN ODCIConst.Success; END; END;

定义函数：

CREATE OR REPLACE FUNCTION f_avg(input NUMBER) RETURN NUMBER PARALLEL_ENABLE AGGREGATE USING f_avg_type;

测试：

SQL> select f_avg(id),avg(id) from "tblabc" 2 ; F_AVG(ID) AVG(ID) ---------- ---------- 276.157895 276.157895