sqlite-main.c

// Copyright 2020 Google LLC.
// SPDX-License-Identifier: Apache-2.0

#include <sqlite3.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct Cursor {
  sqlite3_vtab_cursor c;
  int index;
} Cursor;
int create(sqlite3* xdb, void* x, int y, const char* const* z, sqlite3_vtab** v,
           char** a) {
  sqlite3_declare_vtab(xdb, "CREATE TABLE x(ts INT, dur INT);");
  *v = malloc(sizeof(sqlite3_vtab));
  return SQLITE_OK;
}
int destroy(sqlite3_vtab* v) {
  free(v);
  return SQLITE_OK;
}
int open(sqlite3_vtab* v, sqlite3_vtab_cursor** c) {
  *c = malloc(sizeof(Cursor));
  memset(*c, 0, sizeof(Cursor));
  return SQLITE_OK;
}
int bestindex(sqlite3_vtab* v, sqlite3_index_info* i) {
  int c = 0;
  for (int j = 0; j < i->nConstraint; ++j) {
    if (i->aConstraint[j].usable) i->aConstraintUsage[j].argvIndex = ++c;
  }
  i->orderByConsumed = 1;
  return SQLITE_OK;
}
int filter(sqlite3_vtab_cursor* c, int x, const char* y, int z,
           sqlite3_value** v) {
  return SQLITE_OK;
}
int close(sqlite3_vtab_cursor* c) {
  free(c);
  return SQLITE_OK;
}
int next(sqlite3_vtab_cursor* c) {
  ((Cursor*)c)->index++;
  return SQLITE_OK;
}
int eof(sqlite3_vtab_cursor* c) { return ((Cursor*)c)->index >= 100; }
int column(sqlite3_vtab_cursor* c, sqlite3_context* a, int col) {
  if (col == 0) {
    sqlite3_result_int64(a, ((Cursor*)c)->index * 1e8);
  } else {
    sqlite3_result_int64(a, ((Cursor*)c)->index);
  }
  return SQLITE_OK;
}
int callback(void* noop, int c, char** col, char** name) {
  for (int i = 0; i < c; ++i) printf("%s ", col[i]);
  printf("\n");
  return SQLITE_OK;
}
void MonotoneFn(sqlite3_context* a, int argc, sqlite3_value** argv) {
  sqlite3_result_int64(a, sqlite3_value_int(argv[0]) / ((int64_t)1e9));
}
void run_query(sqlite3* db, const char* query) {
  char* err;
  printf("%s\n", query);
  sqlite3_exec(db, query, &callback, NULL, &err);
  printf("\n");
}
int main(int argc, char** argv) {
  sqlite3* db = NULL;
  sqlite3_initialize();
  sqlite3_open(":memory:", &db);

  sqlite3_module* module = malloc(sizeof(sqlite3_module));
  memset(module, 0, sizeof(*module));
  module->xCreate = &create;
  module->xConnect = &create;
  module->xDisconnect = &destroy;
  module->xDestroy = &destroy;
  module->xOpen = &open;
  module->xClose = &close;
  module->xBestIndex = &bestindex;
  module->xFilter = &filter;
  module->xNext = &next;
  module->xEof = &eof;
  module->xColumn = &column;

  sqlite3_create_function_v2(db, "quantize", 1,
                             SQLITE_DETERMINISTIC | SQLITE_UTF8, NULL,
                             &MonotoneFn, NULL, NULL, NULL);
  sqlite3_create_module_v2(db, "event", module, NULL, NULL);

  run_query(db, "EXPLAIN QUERY PLAN SELECT ts FROM event GROUP BY 1");
  run_query(
      db,
      "EXPLAIN QUERY PLAN SELECT quantize(ts), max(dur) FROM event GROUP BY 1");
  run_query(db,
            "EXPLAIN QUERY PLAN SELECT ts / CAST(1e9 AS int), max(dur) FROM "
            "event GROUP BY 1");
  return 0;
}