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Nullable Columns and Power Query

Chris Webb gives us another reason to curse NULL:

Recently I’ve been asked by colleagues with various different types of performance problems why Power BI is generating SQL in a particular way, and the answer has been the presence of nullable columns in the underlying database – whether it’s SQL Server, Snowflake or Databricks. Now I’m not a DBA or any kind of database tuning expert so I can’t comment on why a SQL query performs the way it does on any given platform, but what I can do is show you two examples of how the presence of nullable columns changes the way Power BI and Power Query generate SQL.

Click through to see what happens.