Provyn Prep · SQL competency
Joins & set logic in the SQL assessment
Joins & set logic is one of the areas a Provyn SQL credential scores separately, so a recruiter can see it on its own rather than averaged into one number. This guide explains what it covers, how it is tested and what to practice.
What it covers
Combining tables correctly: inner and outer joins, self joins, anti-joins and set operations, and spotting when a join silently duplicates or drops rows.
Topics in the practice set for this area
- joins
- set operations
How it is tested
In the timed assessment, questions in this area use these formats: code you write, fill-in-the-blank code, multiple choice, short answer. Each attempt draws its own set of questions, and this area gets its own sub-score on the credential when the attempt includes enough questions from it. The assessment questions themselves are never published; the practice set below is written separately for study.
What to practice
- For each join type, predict the row count of a join on a small table pair, then verify it.
- Find rows in one table with no match in another three ways: LEFT JOIN with IS NULL, NOT EXISTS and EXCEPT.
- Practise explaining why a one-to-many join inflates a SUM, and how to fix it.
Try a practice question
From the free practice set (2 questions in this area). Answers and explanations are in the practice set.
- A LEFT JOIN between Orders and Customers, where no matching Customer exists for a given Order, returns:
- What's the difference between UNION and UNION ALL?
Practice before the real thing
Both are free and use practice questions only, never questions from the real assessment.
More SQL study guides
Last reviewed 2026-10-06.