given this SQL query:
query = "select SESSION_ID from SESSIONS where PLAYER_ID='" + playerId + "' and END_DTS is null";

why does this work:
BasicDBObject condQry = new BasicDBObject("player_id", playerId).append("session_end_dts", 0L);
BasicDBObject fldsQry = new BasicDBObject("session_id", 1);

cur = coll.find(condQry, fldsQry);

but this does not:
query.put("session_id", new BasicDBObject("player_id", playerId)).append("session_end_dts", 0L).append("session_id", 1));
cur = coll.find(query);

??