SQL Interview Questions Every Fresher Must Know

SQL Interview Questions Every Fresher Must Know Work through these 12 questions out loud. Open any question for the full model answer, the trap to avoid, and the follow-up a panel usually asks.

  1. How do Flyway/Liquibase integrate with Spring Boot JPA?

    Prod: spring.jpa.hibernate.ddl-auto=validate, Flyway V1__init.sql through Vn. CI: @Testcontainers PostgreSQL + Flyway migrate + integration tests. Never rename column without...

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  2. What is the N+1 query problem and how do you fix it?

    Loading 100 orders then accessing each order's items triggers 101 queries. Fix with JOIN FETCH in JPQL, @EntityGraph on repository method, or a DTO query selecting only...

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  3. What is Hibernate second-level cache and when enable it?

    Enable for ProductCategory, Currency — READ_ONLY, rarely changed. spring.jpa.properties.hibernate.cache.use_second_level_cache=true with Caffeine region factory. Avoid on...

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  4. How implement multi-tenancy in Spring Security context?

    JWT includes tenant_id — converter sets TenantContextHolder. Base entity @Column tenantId validated on save. Repository methods always include tenant predicate — or Hibernate...

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  5. Saga pattern — choreography vs orchestration?

    Order saga: reserve inventory → charge payment → ship. Failure at payment triggers release inventory compensation. Orchestration clearer for complex flows with visibility....

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  6. Explain the transactional outbox pattern.

    OrderService @Transactional saves Order and OutboxEvent(type=ORDER_CREATED, payload=json). OutboxProcessor @Scheduled polls FOR UPDATE SKIP LOCKED, sends to Kafka, updates...

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  7. What is the difference between ArrayList and LinkedList?

    ArrayList: dynamic array, great for get(i) and iteration, amortized append. LinkedList: node chain, costly random access, only wins for frequent insert/remove in middle with...

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  8. What are text blocks and how do they improve Java code?

    String query = """ SELECT u.id, u.name FROM users u WHERE u.active = true """; — readable without \n concatenation. Use formatted for parameters carefully — prefer...

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  9. Best practices for Spring Data pagination with Pageable?

    Controller: @PageableDefault(size=20, sort="createdAt", direction=DESC) Pageable p. Cap size at 100. Admin reports: keyset pagination on id > lastId for deep pages — OFFSET...

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  10. How does @Transactional work?

    Spring creates a proxy around @Transactional beans. Calling createOrder() from another bean starts a transaction on the thread-bound EntityManager; commit on success, rollback...

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  11. How do Spring application events work with @EventListener?

    OrderService publishes OrderCreatedEvent after save. EmailListener @EventListener sends confirmation. @TransactionalEventListener(AFTER_COMMIT) prevents email on rolled-back...

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  12. When use @Query native SQL vs JPQL in Spring Data JPA?

    JPQL for standard entity fetches and portable logic. Native for PostgreSQL-specific jsonb queries, recursive CTEs, or performance-tuned index hints after EXPLAIN. Interface...

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