Speeding Up Large Joins | Dataford Interview Questions

What would you suggest to speed up joins on large data sets?

Asked in the online SQL technical challenge stage. 6th question of the offline challenge; first five were typical SQL query questions.

You are given two AWS billing tables and need to compare join patterns. Write a SQL query that returns the join performance guidance for each join pattern in the sample data.

Output

One row per join pattern
Columns: join_pattern, recommended_action, reason
Include only rows where the pattern is active
Sort by join_pattern ascending

Schema

join_patterns

Column	Type	Description
pattern_idPK	INT	Primary key for the join pattern
join_pattern	VARCHAR(50)	Short name for the join pattern
estimated_rows_after_join	BIGINT	Estimated number of rows produced by the join
is_active	BOOLEAN	Whether the pattern is currently relevant

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Problem