SQL Value Swapping | Dataford Interview Questions

Write a SQL query to swap values between two columns or rows.

Use the provided PostgreSQL tables. Swap the two assignment value columns only for assignments referenced by approved swap requests. Preserve all other assignments and return the values before and after the swap.

Output

One row per updated assignment, ordered by assignment_id.
Return assignment_id, old_primary_value, old_secondary_value, new_primary_value, and new_secondary_value.

Schema

assignments

Column	Type	Description
assignment_idPK	INT	Unique assignment identifier
primary_value	VARCHAR(50)	First value eligible for swapping
secondary_value	VARCHAR(50)	Second value eligible for swapping

swap_requests

Column	Type	Description
request_idPK	INT	Unique swap request identifier
assignment_id	INT	Assignment targeted by the request
approved	BOOLEAN	Whether the swap request is approved

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Problem