Primary key

The Primary Key (PK) is the set of fields that uniquely identify a row in your table.

Concrete examples:

Daily metrics table (fact table)

Primary Key: (date, campaign_id, ad_id)

date	campaign_id	ad_id	impressions	clicks
2025-01-15	camp_123	ad_456	1000	50
2025-01-15	camp_123	ad_789	800	30

Each combination (date + campaign_id + ad_id) identifies a unique row.

Campaign attributes table (dimension table)

Primary Key: (campaign_id)

campaign_id	name	status	budget
camp_123	Summer Campaign	ACTIVE	5000
camp_456	Winter Campaign	PAUSED	3000

Each campaign_id identifies a unique campaign.

Why is this important?

The Primary Key concept allows you to define which table attributes identify each row as unique. This is essential for:

• Determining the behavior of the UPSERT method: should an existing row be updated or should a new row be inserted?

• Avoiding duplicates in your tables

• Guaranteeing the uniqueness of each row and data integrity, two essential concepts in data management