[All skill tests](https://jobicy.com/tests.md) Skill assessment # PostgreSQL Index Design and Query Plan Analysis Skills Test Evaluate how well you design PostgreSQL indexes and interpret query execution plans. The test focuses on matching index structures to query predicates, joins, ordering, and data distribution. [Start the test](#test-start) Share Assessment setup Ready ## Choose the level that matches your current experience. * 01 Basic Available * 02 Intermediate Available * 03 Advanced Available Instant result Review your score after submission 20–30 Questions per assessment 15–45 min Estimated completion time 3 levels Choose your difficulty SQL & Databases [View category](https://jobicy.com/test-category/sql-basics-for-analysts.md) Start assessment ## Choose your level and begin. Answer without outside help so the result reflects your current knowledge. You will see your score after completing the selected assessment. Efficient PostgreSQL queries depend on understanding how the planner estimates work and chooses access paths. This assessment covers index selection, composite index ordering, plan operators, statistics, and practical tuning decisions that reduce unnecessary reads and sorting. Basic Intermediate Advanced This is a demo version of the test. You may attempt up to 3 questions. To take the full test and save your results, please [log in](https://jobicy.com/dashboard-page.md) or [create an account](https://jobicy.com/dashboard-page#tab2.md). This is a demo version of the test. You may attempt up to 3 questions. To take the full test and save your results, please [log in](https://jobicy.com/dashboard-page.md) or [create an account](https://jobicy.com/dashboard-page#tab2.md). This is a demo version of the test. You may attempt up to 3 questions. To take the full test and save your results, please [log in](https://jobicy.com/dashboard-page.md) or [create an account](https://jobicy.com/dashboard-page#tab2.md). Test details ## Know what to expect. Review the instructions, covered skills, example question themes, and intended audience before beginning. 01 ### Instructions and covered skills Read each query pattern and plan detail carefully before choosing an answer. Keep your attention on PostgreSQL behavior rather than assumptions from another database system. Turn off notifications and avoid switching between unrelated tasks while completing the test. Consider the predicate, join condition, ordering requirement, and expected row count together. Choose the option that best explains the planner behavior or supports the stated workload. Review wording for details such as equality filters, range filters, and included columns before submitting a response. ### Key Areas This test evaluates practical PostgreSQL performance work centered on index design and execution-plan interpretation. Candidates analyze B-tree, GIN, GiST, BRIN, expression, partial, covering, and composite indexes in relation to concrete query patterns. They identify when an index can support equality predicates, range conditions, joins, ordering, grouping, and selective filters. They also recognize the significance of column order in composite B-tree indexes and the tradeoffs involved in adding included columns. The assessment covers reading output from EXPLAIN and EXPLAIN ANALYZE. Candidates should understand scan nodes, join nodes, sort nodes, aggregate nodes, materialization, and bitmap operations. They should be able to compare estimated rows with actual rows, identify signs of stale or insufficient statistics, and distinguish planning time from execution time. Questions also address visibility-map effects on index-only scans, heap fetches, and why a sequential scan may be an appropriate plan for a large portion of a table. ### Recommended Preparation Prepare by creating representative tables and loading data with uneven distributions, duplicate values, nullable fields, and time-based columns. Run queries with EXPLAIN (ANALYZE, BUFFERS) before and after adding indexes, then compare node costs, actual rows, buffer activity, and elapsed execution time. Practice designing indexes from query requirements rather than creating an index for every column. Pay particular attention to equality predicates before range predicates in composite B-tree keys and to the conditions that permit ordered index scans. Review PostgreSQL documentation for planner statistics, ANALYZE, extended statistics, index types, partial-index predicates, and operator classes. Work through plans involving nested loop, hash, and merge joins, and observe how table size, selectivity, available indexes, and memory settings can influence choices. The most useful preparation is repeated comparison of a query's logical requirements with the physical work shown in its plan. 02 ### Examples of questions 1. Which PostgreSQL command displays a query plan with actual row counts and timing information? 2. Why can a composite B-tree index support an equality predicate on its leading column? 3. What does a sequential scan indicate in a PostgreSQL execution plan? 4. Which index type is commonly used for containment searches on JSONB values? 5. When can an index-only scan avoid reading table heap pages? 6. What planner estimate can cause PostgreSQL to select an inefficient join strategy? 7. Which composite index order best supports equality filtering followed by range filtering? 8. What does a high "Rows Removed by Filter" value suggest about a scan? 9. When is a partial index a suitable design choice? 10. What does the Sort node in a query plan represent? 03 ### Who this test is best for Database developers, backend engineers, data engineers, and analysts who write and tune PostgreSQL queries. Related assessments ## Continue with a similar skill test. Explore assessments from the same professional area to compare adjacent skills and build a broader picture of your knowledge. [SQL & Databases 3 levelsSQL JOINs and Multi-Table Queries Skills TestMaster the art of combining data from multiple tables using SQL JOINs. 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