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User-defined aggregate functions
Applies to ✅ Open Source Edition ✅ Express Edition ✅ Professional Edition ✅ Enterprise Edition
Some databases support user-defined aggregate functions, which can then be used along with GROUP BY clauses or as window functions. An example for such a database is Oracle. With Oracle, you can define the following OBJECT type (the example was taken from the Oracle 11g documentation):
CREATE TYPE U_SECOND_MAX AS OBJECT
(
MAX NUMBER, -- highest value seen so far
SECMAX NUMBER, -- second highest value seen so far
STATIC FUNCTION ODCIAggregateInitialize(sctx IN OUT U_SECOND_MAX) RETURN NUMBER,
MEMBER FUNCTION ODCIAggregateIterate(self IN OUT U_SECOND_MAX, value IN NUMBER) RETURN NUMBER,
MEMBER FUNCTION ODCIAggregateTerminate(self IN U_SECOND_MAX, returnValue OUT NUMBER, flags IN NUMBER) RETURN NUMBER,
MEMBER FUNCTION ODCIAggregateMerge(self IN OUT U_SECOND_MAX, ctx2 IN U_SECOND_MAX) RETURN NUMBER
);
CREATE OR REPLACE TYPE BODY U_SECOND_MAX IS
STATIC FUNCTION ODCIAggregateInitialize(sctx IN OUT U_SECOND_MAX)
RETURN NUMBER IS
BEGIN
SCTX := U_SECOND_MAX(0, 0);
RETURN ODCIConst.Success;
END;
MEMBER FUNCTION ODCIAggregateIterate(self IN OUT U_SECOND_MAX, 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 U_SECOND_MAX, returnValue OUT NUMBER, flags IN NUMBER) RETURN NUMBER IS
BEGIN
RETURNVALUE := SELF.SECMAX;
RETURN ODCIConst.Success;
END;
MEMBER FUNCTION ODCIAggregateMerge(self IN OUT U_SECOND_MAX, ctx2 IN U_SECOND_MAX) 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;
The above OBJECT type is then available to function declarations as such:
CREATE FUNCTION SECOND_MAX (input NUMBER) RETURN NUMBER PARALLEL_ENABLE AGGREGATE USING U_SECOND_MAX;
Using the generated aggregate function
jOOQ's code generator will detect such aggregate functions and generate them differently from regular user-defined functions. They implement the org.jooq.AggregateFunction type, as mentioned in the manual's section about aggregate functions. Here's how you can use the SECOND_MAX() aggregate function with jOOQ:
-- Get the second-latest publishing date by author SELECT SECOND_MAX(PUBLISHED_IN) FROM BOOK GROUP BY AUTHOR_ID
// Routines.secondMax() can be static-imported
create.select(secondMax(BOOK.PUBLISHED_IN))
.from(BOOK)
.groupBy(BOOK.AUTHOR_ID)
.fetch();
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