How to make an existing column NOT NULL in AWS REDSHIFT? - amazon-redshift

Question

I had dynamically created a table through glue job and it is successfully working fine. But as per new requirement, I need to add a new column which generates unique values and should be primary key in redshift.
I had implemented the same using rownum() function and it’s working fine. But the latest requirement is that particular column should be primary key.
When I try to do that, it asks the column to have not null. Do you know how to make the column not null dynamically through glue job ? Or any redshift query to make it not null.
I tried all the ways without luck.
w = Window().orderBy(lit('A'))
df = timestampedDf.withColumn("row_num", row_number().over(w))
rowNumDf = DynamicFrame.fromDF(df1, glueContext, "df1")
postStep = "begin; ALTER TABLE TAB_CUSTOMER_DATA ALTER COLUMN row_num INTEGER NOT NULL; ALTER TABLE TAB_CUSTOMER_DATA ADD CONSTRAINT PK_1 PRIMARY KEY (row_num); end;"
## #type: DataSink
## #args: [catalog_connection = "REDSHIFT_CONNECTION", connection_options = {"dbtable": "tab_customer_data", "database": "randomdb"}, redshift_tmp_dir = TempDir, transformation_ctx = "datasink4"]
## #return: datasink4
## #inputs: [frame = rowNumDf]
datasink4 = glueContext.write_dynamic_frame.from_jdbc_conf(frame = rowNumDf, catalog_connection = "REDSHIFT_CONNECTION", connection_options = {"dbtable": "TAB_CUSTOMER_DATA", "database": "randomdb", "postactions": postStep}, redshift_tmp_dir = args["TempDir"], transformation_ctx = "datasink4")
job.commit()

Answer 1

I had solved this using below link approach:
add a new Column with default and not null.
update the old column values to new column.
drop an old column.
make this new column primary.
https://ubiq.co/database-blog/how-to-remove-not-null-constraint-in-redshift/