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From DuyHai Doan <doanduy...@gmail.com>
Subject Re: Maximum number of columns in a table
Date Thu, 15 Sep 2016 18:09:47 GMT
"But I need rows together to work with them (indexing etc)"

What do you mean rows together ? You mean that you want to fetch a single
row instead of 1 row per property right ?

In this case, the map might be the solution:

CREATE TABLE generic_with_maps(
   object_id uuid
   boolean_map map<text, boolean>
   text_map map<text, text>
   long_map map<text, long>,
   ...
   PRIMARY KEY(object_id)
);

The trick here is to store all the fields of the object in different map,
depending on the type of the field.

The map key is always text and it contains the name of the field.

Example

{
   "id": xxxx,
    "name": "John DOE",
    "age":  32,
    "last_visited_date":  "2016-09-10 12:01:03",
}

INSERT INTO generic_with_maps(id, map_text, map_long, map_date)
VALUES(xxx, {'name': 'John DOE'}, {'age': 32}, {'last_visited_date':
'2016-09-10
12:01:03'});

When you do a select, you'll get a SINGLE row returned. But then you need
to extract all the properties from different maps, not a big deal

On Thu, Sep 15, 2016 at 7:54 PM, Dorian Hoxha <dorian.hoxha@gmail.com>
wrote:

> @DuyHai
> Yes, that's another case, the "entity" model used in rdbms. But I need
> rows together to work with them (indexing etc).
>
> @sfespace
> The map is needed when you have a dynamic schema. I don't have a dynamic
> schema (may have, and will use the map if I do). I just have thousands of
> schemas. One user needs 10 integers, while another user needs 20 booleans,
> and another needs 30 integers, or a combination of them all.
>
> On Thu, Sep 15, 2016 at 7:46 PM, DuyHai Doan <doanduyhai@gmail.com> wrote:
>
>> "Another possible alternative is to use a single map column"
>>
>> --> how do you manage the different types then ? Because maps in
>> Cassandra are strongly typed
>>
>> Unless you set the type of map value to blob, in this case you might as
>> well store all the object as a single blob column
>>
>> On Thu, Sep 15, 2016 at 6:13 PM, sfescape@gmail.com <sfescape@gmail.com>
>> wrote:
>>
>>> Another possible alternative is to use a single map column.
>>>
>>>
>>> On Thu, Sep 15, 2016 at 7:19 AM Dorian Hoxha <dorian.hoxha@gmail.com>
>>> wrote:
>>>
>>>> Since I will only have 1 table with that many columns, and the other
>>>> tables will be "normal" tables with max 30 columns, and the memory of 2K
>>>> columns won't be that big, I'm gonna guess I'll be fine.
>>>>
>>>> The data model is too dynamic, the alternative would be to create a
>>>> table for each user which will have even more overhead since the number of
>>>> users is in the several thousands/millions.
>>>>
>>>>
>>>> On Thu, Sep 15, 2016 at 3:04 PM, DuyHai Doan <doanduyhai@gmail.com>
>>>> wrote:
>>>>
>>>>> There is no real limit in term of number of columns in a table, I
>>>>> would say that the impact of having a lot of columns is the amount of
meta
>>>>> data C* needs to keep in memory for encoding/decoding each row.
>>>>>
>>>>> Now, if you have a table with 1000+ columns, the problem is probably
>>>>> your data model...
>>>>>
>>>>> On Thu, Sep 15, 2016 at 2:59 PM, Dorian Hoxha <dorian.hoxha@gmail.com>
>>>>> wrote:
>>>>>
>>>>>> Is there alot of overhead with having a big number of columns in
a
>>>>>> table ? Not unbounded, but say, would 2000 be a problem(I think that's
the
>>>>>> maximum I'll need) ?
>>>>>>
>>>>>> Thank You
>>>>>>
>>>>>
>>>>>
>>>>
>>
>

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