Many-to-Many Efficient Joins | Dataford Interview Questions

How would you join two large datasets with a many-to-many relationship efficiently?

Use the relationship table to connect the datasets and ensure duplicate relationship rows do not inflate the results. Return every row from the first dataset, including rows with no matches.

Output

One row per row in dataset_a
Columns: a_id, a_name, matched_b_count, and total_measure
Include unmatched dataset_a rows with zero values
Order by a_id ascending

Schema

dataset_a

Column	Type	Description
a_idPK	INT	Primary identifier for the first dataset
a_name	VARCHAR(100)	Name associated with the first dataset row

dataset_b

Column	Type	Description
b_idPK	INT	Primary identifier for the second dataset
b_name	VARCHAR(100)	Name associated with the second dataset row
measure	DECIMAL(12,2)	Numeric value to aggregate for matched rows

a_b_links

Column	Type	Description
link_idPK	INT	Primary identifier for a relationship row
a_id	INT	Referenced identifier from dataset_a
b_id	INT	Referenced identifier from dataset_b

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