Exam Certified Associate Developer for Apache Spark topic 1 question 55 discussion

Cross Join in PySpark: A cross join (also known as a Cartesian product) returns the Cartesian product of the two DataFrames, meaning every row from the first DataFrame is paired with every row from the second DataFrame. In PySpark, the crossJoin() method is used specifically for this type of join.

The correct identification of the error is: C. A cross join is not implemented by the DataFrame.join() operation – the DataFrame.crossJoin() operation should be used instead. Explanation: In Spark, to perform a cross join between two DataFrames, you should use the crossJoin() method, not the join() method with the "cross" argument.

Correct answer C from pyspark.sql import Row df = spark.createDataFrame( [(14, "Tom"), (23, "Alice"), (16, "Bob")], ["age", "name"]) df2 = spark.createDataFrame( [Row(height=80, name="Tom"), Row(height=85, name="Bob")]) df.crossJoin(df2.select("height")).select("age", "name", "height").show() https://spark.apache.org/docs/latest/api/python/reference/pyspark.sql/api/pyspark.sql.DataFrame.crossJoin.html

D is the answer here as key is missing. As per syntax, key is needed.

C is correct. # https://spark.apache.org/docs/3.1.1/api/python/reference/api/pyspark.sql.DataFrame.crossJoin.html a = spark.createDataFrame([(1, 2), (3, 4)], ['column1', 'column2']) b = spark.createDataFrame([(5, 6), (7, 8)], ['column3', 'column4']) df = a.crossJoin(b) display(df)

I know it looks confusing to have key column for cross join, but it ijoin method syntaxis: https://spark.apache.org/docs/3.1.2/api/python/reference/api/pyspark.sql.DataFrame.join.html see example below : dataA = [Row(column1=1, column2=2), Row(column1=2, column2=4), Row(column1=3, column2=6)] dfA = spark.createDataFrame(dataA) # Sample data for DataFrame 'b' dataB = [Row(column1=1, column2=2), Row(column1=2, column2=5), Row(column1=3, column2=4)] dfB = spark.createDataFrame(dataB) joinedDF = dfA.join(dfB, on=None, how="cross") joinedDF.show() it is possible to do Cross join this way as well DataFrame.crossJoin() but answer C states that df.join () doesn't do cross, which is wrong.

C. A cross join is not implemented by the DataFrame.join()operation – the DataFrame.crossJoin()operation should be used instead.

cross join doesn't need a key. Answer is C

Key is missing. Answer is D.