22 User-Defined Aggregate Functions Interface

This chapter describes the routines that need to be implemented to define a user-defined aggregate function. The routines are implemented as methods in an object type. Then the CREATE FUNCTION statement is used to actually create the aggregate function.

This chapter contains the following topics:

User-Defined Aggregate Functions

User-Defined Aggregate Functions

The methods in this section are implemented as methods in an object type. The CREATE FUNCTION statement is used to actually create the aggregate function. Table 22-1 summarizes these functions.

Table 22-1 Summary of User-Defined Aggregate Functions

Function	Description
ODCIAggregateInitialize()	Initializes the aggregation context and instance of the implementation object type, and returns it as an `OUT` parameter.
ODCIAggregateIterate()	Iterates through input rows by processesing the input values, updating and then returning the aggregation context.
ODCIAggregateMerge()	Merges two aggregation contexts into a single object instance during either serial or parallel evaluation of the user-defined aggregate.
ODCIAggregateTerminate()	Calculates the result of the aggregate computation and performs all necessary cleanup, such as freeing memory.
ODCIAggregateDelete()	Removes an input value from the current group.
ODCIAggregateWrapContext()	Integrates all external pieces of the current aggregation context to make the context self-contained.

ODCIAggregateInitialize()

Initializes the aggregation context and instance of the implementation object type, and returns it as an OUT parameter. F Implement this routine as a static method.

Syntax

STATIC FUNCTION ODCIAggregateInitialize(
   actx IN OUT <impltype>) 
RETURN NUMBER

Parameter	In/Out	Description
actx	IN OUT	The aggregation context that is initialized by the routine. This value is `NULL` for regular aggregation cases. In aggregation over windows, `actx` is the context of the previous window. This object instance is passed in as a parameter to the next aggregation routine.

Returns

ODCIConst.Success on success, or ODCIConst.Error on error.

ODCIAggregateIterate()

Iterates through input rows by processesing the input values, updating and then returning the aggregation context. Invoked for each value, including NULLs. This is a mandatory routine and is implemented as a member method.

Syntax

MEMBER FUNCTION ODCIAggregateIterate(
   self IN OUT <impltype>, 
   val <inputdatatype>) RETURN NUMBER;

Parameter	IN/OUT	Description
self	IN OUT	As input, the value of the current aggregation context; as output, the updated value.
val	IN	The input value which is being aggregated.

Returns

ODCIConst.Success on success, or ODCIConst.Error on error.

ODCIAggregateMerge()

Merges two aggregation contexts into a single object instance during either serial or parallel evaluation of the user-defined aggregate. This is a mandatory routine and is implemented as a member method.

Syntax

MEMBER FUNCTION ODCIAggregateMerge(
   self IN OUT <impltype>, 
   ctx2 IN <impltype>) RETURN NUMBER;

Parameter	IN/OUT	Description
self	IN OUT	On input, the value of the first aggregation context; on output, the resulting value of the two merged aggregation contexts.
ctx2	IN	The value of the second aggregation context.

Returns

ODCIConst.Success on success, or ODCIConst.Error on error.

ODCIAggregateTerminate()

Calculates the result of the aggregate computation and performs all necessary cleanup, such as freeing memory. Invoked by Oracle as the last step of aggregate computation. This is a mandatory routine and is implemented as a member method.

Syntax

MEMBER FUNCTION ODCIAggregateTerminate(
   self IN <impltype>, 
   ReturnValue OUT <return_type>, 
   flags IN number) RETURN NUMBER;

Parameter	IN/OUT	Description
self	IN	The value of the aggregation context.
ctx2	OUT	The resultant aggregation value.
flags	IN	A bit vector that indicates various options. A set bit of `ODCI_AGGREGATE_REUSE_CTX` indicates that the context will be reused and any external context should not be freed.

Returns

ODCIConst.Success on success, or ODCIConst.Error on error.

See Aso:

"Reusing the Aggregation Context for Analytic Functions" on page 11-6 for details on setting the ODCI_AGGREGATE_REUSE_CTX flag bit.

ODCIAggregateDelete()

Removes an input value from the current group. The routine is invoked by Oracle by passing in the aggregation context and the value of the input to be removed during It processes the input value, updates the aggregation context, and returns the context. This is an optional routine and is implemented as a member method.

Syntax

MEMBER FUNCTION ODCIAggregateDelete(
   self IN OUT <impltype>, 
   val <inputdatatype>) RETURN NUMBER;

Parameter	IN/OUT	Description
self	IN OUT	As input, the value of the current aggregation context; as output, the updated value.
val	IN	The input value which is being removed from the current group.

Returns

ODCIConst.Success on success, or ODCIConst.Error on error.

ODCIAggregateWrapContext()

Integrates all external pieces of the current aggregation context to make the context self-contained. Invoked by Oracle if the user-defined aggregate has been declared to have external context and is transmitting partial aggregates from slave processes. This is an optional routine and is implemented as a member method.

Syntax

MEMBER FUNCTION ODCIAggregateWrapContext(
   self IN OUT <impltype>) RETURN NUMBER;

Parameter	IN/OUT	Description
self	IN	On input, the value of the current aggregation context; on output, the self-contained combined aggregation context.

Returns

ODCIConst.Success on success, or ODCIConst.Error on error.