I need to add additional columns to a table in cassandra. But the existing table is not empty. Is there any way to update it in a simple way? Otherwise what is the best approach to add additional columns to a non empty table? thx in advance.
There's a good example of adding table columns to an existing table in the CQL documentation on ALTER. The following statement will add the column gravesite (with type varchar) to to the table addamsFamily:
ALTER TABLE addamsFamily ADD gravesite varchar;
Related
According to Athena docs, I can not add the date column to an existing table, so I am trying to use the workaround they propose with the timestamp datatype.
But when I run the ALTER TABLE my_table ADD COLUMNS (date_column TIMESTAMP) query, I still get the following error :
Parquet does not support date. See HIVE-6384
Is there any option to add date or timestamp columns to an existing table?
Thanks
UPD: I found out that I can still add timestamp columns with glue UI interface/API
UPD 2: The issue occurs only with one specific table, but it works for others.
You can use the following query to add a timestamp column to an existing table:
ALTER TABLE my_table ADD COLUMNS (date_column TIMESTAMP);
This should work for both Parquet and ORC tables.
I have a table in Cassandra say employee(id, email, role, name, password) with only id as my primary key.
I want to ...
1. Add another column (manager_id) in with a default value in it
I know that I can add a column in the table but there is no way i can provide a default value to that column through CQL. I can also not update the value for manager_id later since I need to know the id (Partition key and the values are randomly generated unique values which i don't know) to update the row. Is there any way I can achieve this?
2. Rename this table to all_employee.
I also know that its not allowed to rename a table in cassandra. So I am trying to copy the data of table(employee) to csv and copy from csv to new table (all_employee) and deleting the old table(employee). I am doing this through an automated script with cql queries in it and script works fine but will fail if it gets executed again(Which i can not restrict) since the table employee will not be there once its deleted. Essentially I am looking for "If exists" clause in COPY query which is not supported in cql. Is there any other way I can achieve the outcome?
Please note that the amount of data in the table is very small so performance in not an issue.
For #1
I dont think cassandra support default column . You need to do that from your appliaction. Write some default value every time you insert a row.
For #2
you can check if the table exists before trying to copy from it.
SELECT your_table_name FROM system_schema.tables WHERE keyspace_name='your_keyspace_name';
Hi I just added a new column Business_sys to my table my_table:
ALTER TABLE my_table ALTER business_sys TYPE set<text>;
But again I just droped this column name because I wanted to change the type of column:
ALTER TABLE my_table DROP business_sys;
Again when I tried to add the same colmn name with different type am getting error message
"Cannnot add a collection with the name business_sys because the collection with the same name and different type has already been used in past"
I just tried to execute this command to add a new column with different type-
ALTER TABLE my_table ADD business_sys list<text>;
What did I do wrong? I am pretty new to Cassandra. Any suggestions?
You're running into CASSANDRA-6276. The problem is when you drop a column in Cassandra that the data in that column doesn't just disappear, and Cassandra may attempt to read that data with its new comparator type.
From the linked JIRA ticket:
Unfortunately, we can't allow dropping a component from the comparator, including dropping individual collection columns from ColumnToCollectionType.
If we do allow that, and have pre-existing data of that type, C* simply wouldn't know how to compare those...
...even if we did, and allowed [users] to create a different collection with the same name, we'd hit a different issue: the new collection's comparator would be used to compare potentially incompatible types.
The JIRA suggests that this may not be an issue in Cassandra 3.x, but I just tried it in 3.0.3 and it fails with the same error.
What did I do wrong? I am pretty new to Cassandra. Any suggestions?
Unfortunately, the only way around this one is to use a different name for your new list.
EDIT: I've tried this out in Cassandra and ended up with inconsistent missing data. Best way to proceed is to change the column name as suggested in CASSANDRA-6276. And always follow documentation guidelines :)
-WARNING-
According to this comment from CASSANDRA-6276, running the following workaround is unsafe.
Elaborating on #masum's comment - it's possible to work around the limitation by first recreating the column with a non-collection type such as an int. Afterwards, you can drop and recreate again using the new collection type.
From your example, assuming we have a business_sys set:
ALTER TABLE my_table ADD business_sys set<text>;
ALTER TABLE my_table DROP business_sys;
Now re-add the column as int and drop it again:
ALTER TABLE my_table ADD business_sys int;
ALTER TABLE my_table DROP business_sys;
Finally, you can re-create the column with the same name but different collection type:
ALTER TABLE my_table ADD business_sys list<text>;
Cassandra doesn't allow you to recreate a column with the same name and the same datatype, but there is an workaround to fix it.
Once you have dropped the column with SET type, you can recreate it with only another "default" type such as varchar or interger.
After recreating with one of those types, you can drop the column once again and finally recreate with the proper type.
I illustrated it below
ALTER TABLE my_table DROP business_sys; # the drop you've done
ALTER TABLE my_table ADD business_sys varchar; # recreating with another type
ALTER TABLE my_table DROP business_sys; # dropping again
ALTER TABLE my_table ADD business_sys list<text>; # recreating with proper type
I'm a newbie to cassandra. I have a confusion with archival of data. Following is the approach I am trying to implement.
Filter the records to be archived.
Create a new column family
Move the filtered records to the new column family
Delete the filtered records from existing column family
Filter the records to be archived. - Achieved with the use of secondary indexes
Create a new column family Create Query
Move the filtered records to the new column family I thought of implementing this by the approach mentioned in cassandra copy data from one columnfamily to another columnfamily But this copies all the data from column family 1 to 2. Is it possible to move only the filtered rows to new column family?
Delete the filtered records from existing column family I am not sure of how to achieve this in CQL. Please help me.
Additionally, Let me know if there is any better approach.
COPY then DELETE sounds like a valid strategy here.
For deleting rows, take a look at the DELETE command, it takes the same WHERE condition as a SELECT does.
Unfortunately this won't work for a query that requires "ALLOW FILTERING", although there is an enhancement request to add this.
I want to add columns dynamically to this column family via code using cql.
CREATE COLUMN FAMILY blog_entry
WITH comparator = UTF8Type
AND key_validation_class=UTF8Type
AND default_validation_class = UTF8Type;
how shall I do it?
This is becoming something of a FAQ, so I wrote an in-depth explanation: http://www.datastax.com/dev/blog/does-cql-support-dynamic-columns-wide-rows
For this to work you have to first alter the table to add column and then insert will start working. I tried the above on cqlsh and it worked.
alter table newdata add column name varchar;
Please refer below link too:
How to define dynamic column families in cassandra
ALTER TABLE blog_entry ADD newcolumnname text;