Handling Missing Values | Dataford Interview Questions

You are given a dataset with missing values. What steps would you take to handle this?

Using the supplied PostgreSQL tables, write a query that returns a cleaned but auditable application-level dataset. Use explicit treatments for missing categorical and numeric values, while retaining indicators for values that remain unknown.

Output

One row per application, including applications without a matching candidate.
Columns: application_id, candidate_id, candidate_name, location, years_experience, status, salary_expectation, applied_on, and applied_on_missing.
Replace missing names, locations, and statuses with Unknown, replace missing salaries with the non-null median salary, retain unknown experience and dates as NULL, and sort by application_id ascending.

Schema

candidates

Column	Type	Description
candidate_idPK	INT	Unique candidate identifier
candidate_name	VARCHAR(100)	Candidate's name
location	VARCHAR(100)	Candidate's current location
years_experience	INT	Reported years of professional experience

applications

Column	Type	Description
application_idPK	INT	Unique application identifier
candidate_id	INT	Candidate associated with the application
status	VARCHAR(30)	Current application status
salary_expectation	DECIMAL(10,2)	Candidate's expected annual salary
applied_on	DATE	Date the application was submitted

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