As discussed in Aggregate Function Parameter List, the aggregate UDF parameter list includes a pointer to an FNC_Context_t function context structure, which is defined as:
struct FNC_Context_t {
int version;
FNC_flags_t flags;
void *interim1;
int intrm1_length;
void *interim2;
int intrm2_length;
long group_count;
long window_size;
long pre_window;
long post_window;
} FNC_Context_t;
The function should treat the structure as read only, and must never change any of its values. The structure has four members that are used for intermediate storage in aggregate functions.
| Member … | Specifies … |
|---|---|
| interim1 | a pointer to the aggregate storage area in which the function saves intermediate results. |
| interim2 | a pointer to an intermediate storage area to combine with the interim1 storage area when the value of aggregation phase is AGR_COMBINE. |
| intrm1_length | the length of interim1. |
| intrm2_length | the length of interim2. |