Nulls and Precision in SQL | Dataford Interview Questions

How would you handle null values and data type formatting, including ensuring precision in output, in a complex reporting query for HackerRank?

Use the provided HackerRank challenge, domain, and submission data. Include active challenges even when they have no submissions, and represent missing values consistently.

Output

One row per active challenge, ordered by challenge_id ascending.
Return challenge_id, challenge_name, domain_name, total_submissions, average_score, pass_rate_pct, and average_score_display.
Use zero-valued numeric metrics when no applicable submissions exist, and show domain Unassigned when the domain is missing.

Schema

challenges

Column	Type	Description
challenge_idPK	INT	Unique HackerRank challenge identifier
challenge_name	VARCHAR(120)	Challenge display name
domain_id	INT	Optional associated domain
is_active	BOOLEAN	Whether the challenge is currently active

domains

Column	Type	Description
domain_idPK	INT	Unique domain identifier
domain_name	VARCHAR(80)	Challenge domain name

submissions

Column	Type	Description
submission_idPK	INT	Unique submission identifier
challenge_id	INT	Challenge associated with the submission
score	NUMERIC(5,2)	Submission score, which may be missing
status	VARCHAR(20)	Submission result status

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