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Three-Table Join with Business Filters

MediumSQL & Data Manipulation00:00
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Problem

Context

Business analysts often need to combine customer, transaction, and reference data before applying layered business rules. This tests whether you can structure a readable SQL query instead of writing one long, brittle statement.

Question

Explain how you would write a PostgreSQL query that joins three tables and filters the result based on complex business criteria. Your explanation should cover how you choose the join order, how you decide between INNER JOIN and LEFT JOIN, where you place date-based filters, and how you would use CASE WHEN or a CTE to make the logic easier to read.

You can assume a TEKsystems reporting scenario such as joining consultants, assignments, and client accounts to return only active assignments that meet multiple business rules.

Scope Guidance

The interviewer is looking for a medium-depth answer: describe the query structure, explain the filtering logic clearly, and mention common mistakes such as turning a LEFT JOIN into an INNER JOIN accidentally through the WHERE clause.