Error:
RuntimeError: Query defined in function 'functionName' returned 'NoneType'. It must return either a Spark or Koalas DataFrame.
Resolution :-
Check the function/DLT table and verify if this delta table function/Table is returning some dataframe or not since every delta live table should return some dataframe
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Could not materialize 'tableName' because a STREAMING_TABLE table already exists with that name.
Resolution :
As error message clearly indicating that there is some existing streaming table present in the system with the same name using which you are trying to create a materialized view.
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Always remember when you are working with streaming dataset
when dealing with streaming DataFrames in Spark, performing a Left Anti Join where the streaming DataFrame is on the right side of the join operation is not currently supported.
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Resolution:-
you have to ceate a delta live table using @dlt.table as below and then use your code.
@dlt.table(name = "testing")
def testing_data()
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