Join types output with duplicates and nulls | Dataford Interview Questions

Two tables were given with duplicates and NULL values; predict the output of INNER, LEFT, RIGHT and FULL OUTER JOIN

Asked in the Round 1 stage. Write a PostgreSQL query that returns the output of all four joins using table_a and table_b, matching rows on join_key.

Output

Return join_type, both row identifiers, both join keys, and both values.
Include duplicate matches and preserve NULLs produced by unmatched rows.
Order by join type as INNER, LEFT, RIGHT, FULL, then by the available row identifiers.

Schema

table_a

Column	Type	Description
row_idPK	INT	Unique row identifier
join_key	INT	Value used to match rows
value	VARCHAR(50)	Value stored in table_a

table_b

Column	Type	Description
row_idPK	INT	Unique row identifier
join_key	INT	Value used to match rows
value	VARCHAR(50)	Value stored in table_b

Your question is Join types output with duplicates and nulls. Start with the requirements and the two tables in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

Problem