Why do multiple-table joins produce duplicate rows?

When you have related tables you often have one-to-many or many-to-many relationships. So when you join to TableB each record in TableA many have multiple records in TableB. This is normal and expected. Now at times you only need certain columns and those are all the same for all the records, then you would need … Read more

Why does join fail with “java.util.concurrent.TimeoutException: Futures timed out after [300 seconds]”?

This happens because Spark tries to do Broadcast Hash Join and one of the DataFrames is very large, so sending it consumes much time. You can: Set higher spark.sql.broadcastTimeout to increase timeout – spark.conf.set(“spark.sql.broadcastTimeout”, newValueForExample36000) persist() both DataFrames, then Spark will use Shuffle Join – reference from here PySpark In PySpark, you can set the … Read more

Joining multiple tables returns NULL value

That is because null on either side of the addition operator will yield a result of null. You can use ISNULL(LiabilityPremium, 0) Example: ISNULL(l.LiabilityPremium,0) + ISNULL(h.LiabilityPremium,0) as LiabilityPremium or you can use COALESCE instead of ISNULL. COALESCE(l.LiabilityPremium,0) + COALESCE(h.LiabilityPremium,0) as LiabilityPremium Edit I am not sure if this is coincidence with this small data set … Read more