b0ti

  {"foo":"bar"}
  {"foo":"bar2","intfield":42}

  select * from tbl;
  --
  {"_id":1,"eventtime":"2016-07-20 10:37:12","foo":"bar","whatever":"xx"}
  {"_id":2,"eventtime":"2016-07-20 10:38:22","foo":"bar2","intfield":42}

   CREATE TABLE tbl(eventtime datetime);
   INSERT INTO tbl {"eventtime":"2016-07-20 10:37:12","foo":"bar","whatever":"xx"};
   INSERT INTO tbl {"eventtime":"2016-07-20 10:38:22","foo":"bar2","intfield":42};
   SELECT foo, intfield FROM tbl;
   --
   {"foo":"bar","intfield":null}
   {"foo":"bar2","intfield":42}