Here is a cassandra table:
CREATE TABLE Account(
id uuid,
userRef uuid,
name map<text, text>,
dataStatus text,
dataVisibility text,
...
PRIMARY KEY( id, dataStatus, dataVisibility, userRef)
)
CREATE INDEX idx_xxx_account_name ON Account (name);
'name' is a cql3 column of (collection) type 'map'. My question is: is it possible to create secondary index on a map type, i.e., name?
Thanks.
As of Cassandra 1.2.6, custom indexes on collections are supported.
https://git-wip-us.apache.org/repos/asf?p=cassandra.git;a=blob_plain;f=CHANGES.txt;hb=refs/tags/cassandra-1.2.6
Your question is quite old. In cassandra 2.1 valid syntax is
CREATE INDEX on Account(keys(name));
No response? I have decided to rewrite the table as follows:
CREATE TABLE Account(
id uuid,
userRef uuid,
**main_name text,**
**other_name map<text, text>,**
dataStatus text,
dataVisibility text,
...
PRIMARY KEY( id, dataStatus, dataVisibility, userRef)
)
CREATE INDEX idx_xxx_account_name ON Account (main_name);
*_name could be anything e.g., email, phone etc. For example, a main_name could be the mandatory, whereas other_name could be optional.
Anyway now I can index main_name as a 'text' type instead of the map of text values.
To answer your initial question:
There is no support for secondary indexes on collections yet. Concretely, you could associate a set of tags to a user, but you cannot automatically index users by their tags yet. Adding that support is definitively on the roadmap but remains to be implemented.
Coming in 1.2: Collections support in CQL3
Also, I don't quite see why you use a map? Why not a simple set or list? Have a look at the reference provided below.
create index idx_name on Account(ENTRIES(name))
this is for access the rows with particular entry in map.
Related
I have created the following user defined types (UDT) in cassandra :
CREATE TYPE keyspace.location (
latitude text,
longitude text,
accuracy text,
address text
);
CREATE TYPE keyspace.person (
name text,
contact_no text,
alternate_contact text
);
and I want to use these to create another UDT
CREATE TYPE keyspace.pinpoint(
user <person>,
location <location>
);
You can nest UDTs by simply specifying your UDT as the type within another UDT in this manner:
CREATE TYPE keyspace.pinpoint (
user person,
location location
);
You don't enclose them in <> brackets because those are used for collections.
As a side note, I personally wouldn't nest UDTs unless you have no other option. UDTs are not as flexible as native columns. Inserting or updating data in a nested UDT can get very complicated and hard to maintain.
Whenever possible, try to use generic table definitions. For example instead of defining the type pinpoint, try to use a table with native column types and clustered rows. Cheers!
You need to declare these nested UDTs as frozen<UDTName>, like:
CREATE TYPE keyspace.pinpoint(
user frozen<person>,
location frozen<location>
);
But this means that you won't be able to update their individual fields - you'll able only update the whole field, with complete UDT instance, for example, complete user or location.
In Cassandra, I understand that tables are supposed to be created according to what needs to be queried. For example, I currently have a Users and Users_By_Status table.
##Users##
CREATE TABLE Users (
user_id uuid,
name text,
password text,
status int,
username text,
PRIMARY KEY (user_id)
);
CREATE INDEX user_username_idx ON Users (username);
##Users_By_Status##
CREATE TABLE Users_By_Status (
username text,
status int,
user_id uuid,
PRIMARY KEY (username, status, user_id)
);
In this case, if a user leaves, their record won't be deleted. Instead, status will be changed from 1 to 0.
If I insert data into the Users table, do I need to manually insert the data into Users_By_Status table too? What happens if I update the status in Users? Do I need to manually update the record in Users_By_Status table too?
I have a feeling I'm understanding Cassandra wrongly. Appreciate all the help I can get.
Shortly answer: yes, in your case you need to delete manually.
In cassandra db you need to write more code in your app layer to handle cenarios like that.
But we have other options like materialized view or BATCH Statements.
For your solution, i think that materialized view is the best option. You can create a Materialized view from your table Users. Like this:
CREATE MATERIALIZED VIEW Users_By_Status
AS SELECT username, status, userid
FROM Users
PRIMARY KEY(username, status, userid);
And yes, when you update table users, the update will happen in the Materialized View Users_By_Status too.
Reference: https://docs.datastax.com/en/cql-oss/3.3/cql/cql_using/useCreateMV.html
Do I need to manually update the record in Users_By_Status table too?
So CoutinhoBR alluded to it, but I'll come right out and say it. You cannot update primary key values in Cassandra. So that's where a DELETE is required to get the old status value out of there, and then a write for the new one.
When I tried to retrieve table using contains keyword it prompts "Cannot use CONTAINS relation on non collection column col1" but when I tried to create table using
CREATE TABLE test (id int,address map<text, int>,mail list<text>,phone set<int>,primary key (id,address,mail,phone));
it prompts "Invalid collection type for PRIMARY KEY component phone"
One of the basics in Cassandra is that you can't modify primary keys. Always keep that in mind.
You can't use a collection as primary key unless it is frozen, meaning you can't modify it.
This will work
CREATE TABLE test (id int,address frozen<map<text, int>>,mail frozen<list<text>>,phone frozen<set<int>>,primary key (id,address,mail,phone));;
However, I think you should take a look at this document: http://www.datastax.com/dev/blog/cql-in-2-1
You can put secondary indexes on collections after cql 2.1. You may want to use that functionality.
Let say i have this table
CREATE TABLE mykeyspace.post (
id uuid PRIMARY KEY,
title text,
photos set<frozen <photoIds>>
);
and UDT :
CREATE TYPE mykeyspace.photoIds (
photoId uuid,
details text
);
How can I paginated through photos, means 10 photos at a time for given post id ?
Paging through collections is not supported.
See reference manual:
Keep collections small to prevent delays during querying because Cassandra reads a collection in its entirety. The collection is not paged internally.
As discussed earlier, collections are designed to store only a small amount of data.
May I propose another schema for your table post :
CREATE TABLE mykeyspace.post (
id uuid,
title text static,
photo photo,
PRIMARY KEY (id, photo)
);
CREATE TYPE mykeyspace.photo (
id uuid,
details text
);
This schema means :
There is one partition by id => a partition is equivalent to a post
There is one title by partition/post
There is multiple photo ids by partition/post
This schema should serve your goal very well until you reach about 100.000 photos by partition/post.
If you have never used static columns before, you can refer to Datastax documentation
The driver can do the paging for you. See Paging Feature in Datastax Java driver documentation.
The Cql query looks like this :
select photo.id, photo.details from post where id=*your_post_id*;
PS : I think you should not use uppercase in your schema.
I'm trying to provide a service for user validation of table structures, one component of which is column data type, like uuid, text, and bigint in the `CREATE TABLE' statement below.
USE my_keyspace;
CREATE TABLE users (
id uuid,
name text,
age bigint);
If I do
USE system;
SELECT validator FROM schema_columns
WHERE keyspace_name='my_keyspace' AND columnfamily_name='users';
I get
org.apache.cassandra.db.marshal.UUIDType
org.apache.cassandra.db.marshal.UTF8Type
org.apache.cassandra.db.marshal.LongType
Which seems informative, but on closer inspection, multiple distinct datatypes can map to the same validator value. Is there a way I can pull the data type info as entered in the `CREATE TABLE' statement, or at least find some distinction between the types?
Also, I'm curious as to why the validator data has the 'org.apache.cassandra...' prepended to it, and couldn't find an explanation, so if anybody knows why that is, I'd be very interested to know.
Which seems informative, but on closer inspection, multiple distinct datatypes can map to the same validator value.
If this is the case, as for example with varchar and text, I believe that the data types map on one another and are interchangeable. Anyone else correct me if I am wrong.
Is there a way I can pull the data type info as entered in the `CREATE TABLE' statement, or at least find some distinction between the types?
The only way I know would be:
DESC TABLE users;
Also, I'm curious as to why the validator data has the 'org.apache.cassandra...' prepended to it, and couldn't find an explanation, so if anybody knows why that is, I'd be very interested to know.
Cassandra is implemented in Java and this is the full path to the Class that implements the data type.
More info:
http://docs.datastax.com/en/cql/3.0/cql/cql_reference/cql_data_types_c.html
https://github.com/apache/cassandra/tree/trunk/src/java/org/apache/cassandra/db/marshal
Use following query:
select column_name,type from system_schema.columns where keyspace_name ='my_keyspace' AND table_name='users';