"Keith Medcalf" <kmedc...@dessus.com> writes:
> Alternatively, to implement your original question, write an aggregate
> function which returns the first non-null value it comes across, and use the
> negated unix timestamp as an explicit rowid, depending on the fact that a
> table-scan does an in-order traversal of the table btree:
Except for the names, the below code is *exactly*, character by
character, as what I first wrote, but then I realised that the order
of the values going to the step function might not be defined. So can
I trust that I will get the order of my unix time primary key? It
would be convenient if I can omit the timestamp argument in the
function.
>
> typedef struct fnnCtx fnnCtx;
> struct fnnCtx
> {
> double fnn;
> int flag;
> };
>
> SQLITE_PRIVATE void fnnStep(sqlite3_context *context, int argc, sqlite3_value
> **argv)
> {
> fnnCtx* p = sqlite3_aggregate_context(context, sizeof(fnnCtx));
> if (p && sqlite3_value_numeric_type(argv[0]) != SQLITE_NULL && p->flag ==
> 0)
> {
> p->fnn = sqlite3_value_double(argv[0]);
> p->flag = 1;
> }
> }
>
> SQLITE_PRIVATE void fnnFinal(sqlite3_context *context)
> {
> fnnCtx* p = sqlite3_aggregate_context(context, 0);
> if (p && p->flag == 1)
> sqlite3_result_double(context, p->fnn);
> }
--
Steinar Midtskogen
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