200+ SQL Interview Questions

Explore the Oracle dual table, its one row one column, and its use with pseudo columns, arithmetic, and number generation, plus key interview topics on backups and counts.

Explore sql filters by comparing in and equal to operators, the 999 value limit, exist versus in with subqueries, and where versus having for pre- and post-aggregation filtering.

Delete uses a where clause to remove rows and can be rolled back; truncate removes all data fast, cannot be rolled back, and creates no undo log or dependencies.

Explore sql joins, including inner join, left outer join, right outer join, full outer join, and self join, with examples and the effects of missing join conditions.

Explore Oracle data types, including character, numeric, date and timestamp types, large objects and xml type, and compare varchar2 with character, date with timestamp, and composite data types.

Explore Oracle SQL interview questions on functions, including substring versus in string, single row vs multi row, conversion and pad functions, date functions, and case versus decode.

Explore common SQL null handling concepts, including arithmetic with nulls, NVL, NVL2, NULLIF, COALESCE, is null checks, and converting nullable columns to not null.

Explore integrity constraints in Oracle, including not null, primary key, foreign key, check, unique, and references, with practical examples and how to disable or cascade constraints.

Explain on delete cascade behavior and the firing order of before triggers, constraints, and after triggers; discuss circular references and disabling foreign keys to insert data.

Learn what a sequence is, how it auto generates continuous unique numbers, how to create one, and how to reset it with alter sequence and increment by.

Discover how SQL synonyms provide alternative names for tables, views, sequences, and stored procedures, enable cross-schema access via public and private synonyms, and support code switching with underlying object privileges.

Explore set operations such as union, union all, minus, and intersect; compare with joins; learn when duplicates are removed and why performance differs.

Examine subqueries in SQL, including nested and correlated subqueries, inline views, scalar subqueries, and the width clause to reuse results and boost performance.

Explore views in SQL, a virtual table that hides data complexity, masks sensitive columns, and supports updates, deletes, and inserts, including instead of triggers and the force option.

Explore database concepts, including what a database is and the dbms vs rdbms distinction. Examine sql, primary and foreign keys, fields, records, tables, and transactions with commit and rollback.

Understand ACID properties atomicity, consistency, isolation, durability, and how locks—shared or exclusive—manage concurrency, with SGA components library cache, data dictionary cache, database buffer cache, and redo log buffer cache.

Explore Oracle database concepts such as PGA memory per server process, the global area and instance, plus table spaces, data files, data blocks, and the data dictionary.

Explore database concepts including stable fragmentation and its impact on performance, data modeling from conceptual and logical models to physical schemas, er diagrams, and deadlocks in relational databases.

Learn the SQL statement lifecycle from parsing and syntax/semantic checks to shared pool lookup, then optimization and execution that fetches and filters data for display.

Understand how virtual columns are derived at runtime, not stored on disk, and how to index, apply constraints, and partition them with deterministic functions (Oracle 11g+).

Explore index types, from b-tree (default) to bitmap index, bitmap join index, and function-based indexes, and how they affect query performance, usage patterns, and explain plan checks.

Master table partitions to reduce maintenance time and boost query performance by focusing on range, list, hash, interval partitions, plus partition exchange and virtual column based partitioning.

Learn what a materialized view is and why we use them. Examine refresh types (fast, complete, force) and methods (on commit, on demand), differences from views, and query rewrite.

Explore global temporary tables, their session-bound visibility, and how on commit preserve rows affects data during intermediate SQL operations; learn when and why these tables boost performance in queries.

Compare analytical functions with aggregate functions, using window partitioning to compute group values for each row, and explore pivot, unpivot, lag, and lead techniques.

Explore large objects (lobs) for storing multimedia and documents, including internal lobs (blob, clob, nclob) and external lobs (bfile), with transactions and features like temporary, secure, compressed, and encrypted.

Explore Oracle SQL tuning concepts from interview questions, including join methods (merge, nested loop, hash, sort merge), and passing with soft and hard parse.

Explore how arithmetic on indexed columns can suppress index usage, when to rely on index vs full table scans, and how hints, tracing, statistics, and reports optimize Oracle SQL performance.

Learn how to tune a SQL query using explain plan, analyze execution plans, identify index suppression causes, and guide the optimizer with hints to choose the best join method.