Datastax rename table - cassandra

I have deployed 9 node cluster on google cloud.
Created a table and loaded the data. Now want to change the table name.
Is there any way I can change the table name in Cassandra?
Thanks

You can't rename table name.
You have to drop the table and create again
You can use ALTER TABLE to manipulate the table metadata. Do this to change the datatype of a columns, add new columns, drop existing columns, and change table properties. The command returns no results.
Start the command with the keywords ALTER TABLE, followed by the table name, followed by the instruction: ALTER. ADD, DROP, RENAME, or WITH. See the following sections for the information each instruction require
If you need the data you can backup and restore data using copy command in cqlsh.
To Backup data :
COPY old_table_name TO 'data.csv'
To Restore data :
COPY new_table_name FROM 'data.csv'

Related

How to rename column names from lookup in ADF?

I have metadata in my Azure SQL db /csv file as below which has old column name and datatypes and new column names.
I want to rename and change the data type of oldfieldname based on those metadata in ADF.
The idea is to store the metadata file in cache and use this in lookup but I am not able to do it in data flow expression builder. Any idea which transform or how I should do it?
I have reproduced the above and able to change the column names and datatypes like below.
This is the sample csv file I have taken from blob storage which has meta data of table.
In your case, take care of new Data types because if we don't give correct types, it will generate error because of the data inside table.
Create dataset and give this to lookup and don't check first row option.
This is my sample SQL table:
Give the lookup output array to ForEach.
Inside ForEach use script activity to execute the script for changing column name and Datatype.
Script:
EXEC SP_RENAME 'mytable2.#{item().OldName}', '#{item().NewName}', 'COLUMN';
ALTER TABLE mytable2
ALTER COLUMN #{item().NewName} #{item().Newtype};
Execute this and below is my SQL table with changes.

Azure Data flow - presql script, dynamic content

I want to run a presql script in the Data flow in SINK. I want to delete exiting records for particular year.
This particular year will be coming from source excel file.
Say I have a file for 2021 data and loaded that data into DB. when I rerun the pipeline for the same excel file I want to delete 2021 related records in DB and insert fresh. This table may contain multiple years data. So everytime a new file arrives for a particular year, I want to delete that respective records and reload the new data.
I can read the year value from source file column. And I can keep it as derived column. How Can I write a presql script to delete?
delete from where year = <sourcefile.year>
how can i do this in data flow?
Pls help!
You can use a temporary table in sink1 and delete the records in the sink2.
Please follow the demonstration below:
This is my SQL table with a sample data.
Create two SQL sinks for it from same source using a new branch.
In the first sink, provide a dataset with edit table name option for the temporary table.
In sink check on Recreate table.
In sink 2, give your SQL table with the below SQL script.
DELETE FROM exceltable WHERE year in (select year from dbo.temp1)
drop table dbo.temp1;
In the settings of Data flow give the Write order of sinks.
Temporary table sink should execute first.
This is my result in the SQL table after deleting records.

How to overwrite source table azure Data factory

I am new to ADF. I have a pipeline which deletes all rows of any of the attributes are null. Schema : { Name, Value, Key}
I tried using a data flow with Alter Table and set both source and sink to be the same table but it always appends to the table instead of overwriting it which creates duplicate rows and the rows I want to delete still remain. Is there a way to overwrite the table.
Assuming that your table is SQL table, I have tried to overwrite the source table after deleting the specific null values. It successfully deleted the records but got the duplicate records even after exploring various methods.
So, as an alternate you can try the below methods to achieve your requirement:
By Creating new table and deleting old table:
This is my sample source table names mytable.
Alter transformation
Give new table in the sink and in settings->post SQL scripts. give the drop command to delete the source dataset. Now your sink table is your required table. drop table [dbo].[mytable]
Result table(named newtable) and old table.
Source table deleted.
Deleting null values from source table using script activity
Use script activity to delete the null values from source table.
Source table after execution.

why the default auto created sql tables column length is -1 in azure data factory?? and how to make it fixed?

I am trying to read data from csv to azure sql db using copy activity. I have selected auto create option for destination table in sink dataset properties.
copy activity is working fine but all columns are getting created with nvarchar(max) or length -1. I dont want -1 length as default length for my auto created sink table columns.
Does any one know how to change column length or create fixed length columns while auto table creation in azure data factory?
As you have clearly detailed, the auto create table option in the copy data activity is going to create a table with generic column definitions. You can run the copy activity initially in this way and then return to the target table and run T-SQL statements to further define the desired column definitions. There is no option to define table schema with the auto create table option.
ALTER TABLE table_name ALTER COLUMN column_name new_data_type(size);
Clearly, the new column definition(s) must match the data that has been initially copied via the first copy activity but this is how you would combine the auto create table option and resulting in clearly defined column definitions.
It would be useful if you created a Azure Data Factory UserVoice entry to request that the auto create table functionality include creation of column definitions as a means of saving the time needed to go back an manually alter the columns to meet specific requirements, etc.

Adding columns to a sybase table with unique auto_identity index option

I've inherited a Sybase database that has the 'unique auto_identity index' option enabled on it. As part of an upgrade process I need to add a few extra columns to the tables in this database i.e.
alter table mytable add <newcol> float default -1 not null
When I try to do this I get the follow error:
Column names in each table must be unique, column name SYB_IDENTITY_COL in table #syb__altab....... is specifed more than once
Is it possible to add columns to a table with this property enabled?
Update 1:
I created the following test that replicates the problem:
use master
sp_dboption 'esmdb', 'unique auto_identity indexoption',true
use esmdb
create table test_unique_ids (test_col char)
alter table test_unique_ids add new_col float default -1 not null
The alter table command here produces the error. (Have tried this on ASE 15/Solaris and 15.5/Windows)
Update 2:
This is a bug in the Sybase dbisql interface, which the client tools Sybase Central and Interactive SQL use to access the database and it only appears to affect tables with the 'unique auto_identity index' option enabled.
To work around the problem use a different SQL client (via JDBC for example) to connect to the database or use isql on the command line.
Should be no problem to ALTER TABLE with such columns; the err msg indicates the problem regards something else. I need to see the CREATE TABLE DDL.
Even if we can't ALTER TABLE, which we will try first, there are several work-arounds.
Responses
Hah! Internal Sybase error. Open a TechSupport case.
Workaround:
Make sure you get jthe the exact DDL. sp_help . Note the IDENTITY columns and indices.
Create a staging table, exactly the same. Use the DDL from (1). Exclude the Indices.
INSERT new_table SELECT old_table. If the table is large, break it into batches of 1000 rows per batch.
Now create the Indices.
If the table is very large, AND time is an issue, then use bcp. You need to research that first, I am happy to answer questions afterwards.
When I ran your sample code I first get the error:
The 'select into' database option is not enabled for database 'mydb'. ALTER TABLE with data copy cannot be done. Set the 'select into' database option and re-run
This is no doubt because the data within your table needs copying out because the new column is not null. This will use tempdb I think, and the error message you've posted refers to a temp table. Is it possible that this dboption has been accidentally enabled for the tempdb?
It's a bit of a shot in the dark, as I only have 12.5 to test on here, and it works for me. Or it could be a bug.

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