261. What is the purpose of SQL's MATCH_RECOGNIZE clause?
- a) Pattern matching in time-series data
- b) String similarity comparison
- c) Regular expression validation
- d) Data encryption
Answer: A - Identifies patterns across ordered rows (Oracle, Snowflake).
262. Which SQL feature enables incremental materialized view refreshes?
- a) FAST REFRESH
- b) INCREMENTAL UPDATE
- c) PARTIAL REBUILD
- d) DELTA SYNCHRONIZATION
Answer: A - Only processes changed data (Oracle, PostgreSQL).
263. What does SQL's TIME TRAVEL feature provide?
- a) Query historical data
- b) Timezone conversion
- c) Query execution time estimation
- d) Temporal table joins
Answer: A - Access data at past points in time (Snowflake, SQL Server).
264. Which database provides native blockchain tables?
- a) Oracle Database
- b) SQL Server
- c) PostgreSQL
- d) MySQL
Answer: A - Immutable tables with cryptographic hashes.
265. What is the purpose of SQL's GENERATE_SERIES function?
- a) Create number sequences
- b) Generate test data
- c) Expand date ranges
- d) All of the above
Answer: D - Useful for filling gaps in time-series data (PostgreSQL, SQL Server).
266. Which SQL feature enables zero-copy cloning?
- a) CREATE CLONE
- b) COPY FREE
- c) SHALLOW DUPLICATE
- d) Implementation-specific syntax
Answer: D - Snowflake uses CLONE, Oracle uses SNAPSHOT.
267. What is the purpose of SQL's APPROXIMATE DISTINCT functions?
- a) Faster unique value counting
- b) Estimate data skew
- c) Sample-based analysis
- d) All of the above
Answer: A - Trade precision for performance (HyperLogLog algorithm).
268. Which database provides native geospatial machine learning?
- a) PostgreSQL with PostGIS
- b) Oracle Spatial
- c) SQL Server with ML Services
- d) All of the above
Answer: D - Location-aware model training and prediction.
269. What is the purpose of SQL's SESSION_PARAMETER function?
- a) View current connection settings
- b) Change runtime configurations
- c) Audit parameter changes
- d) All of the above
Answer: A - Snowflake's context function.
270. Which feature enables cross-cloud SQL queries?
- a) Database links
- b) Data virtualization
- c) Federated queries
- d) All of the above
Answer: D - Query across AWS, Azure, GCP without data movement.
271. What is the purpose of SQL's STREAM object?
- a) Change data capture
- b) Continuous query processing
- c) Real-time analytics
- d) All of the above
Answer: D - Snowflake's event tracking mechanism.
272. Which database provides native time-series forecasting?
- a) Oracle Database
- b) SQL Server
- c) PostgreSQL with TimescaleDB
- d) All of the above
Answer: D - Built-in ARIMA, exponential smoothing models.
273. What is the purpose of SQL's RESULT_SCAN function?
- a) Reuse previous query results
- b) Validate output correctness
- c) Scan for sensitive data
- d) Estimate result size
Answer: A - Snowflake's query result caching.
274. Which feature enables SQL queries on blockchain data?
- a) Oracle Database Blockchain Tables
- b) SQL Server Ledger
- c) PostgreSQL pg_chain
- d) All of the above
Answer: D - Query immutable ledger data with standard SQL.
275. What is the purpose of SQL's EXTERNAL TABLE feature?
- a) Query files without loading
- b) Access cloud storage
- c) Federate queries
- d) All of the above
Answer: D - Process CSV, Parquet, etc. directly.
276. Which database provides native graph pattern matching?
- a) Oracle PGQL
- b) SQL Server Graph
- c) PostgreSQL with Apache Age
- d) All of the above
Answer: D - Find paths/relationships using SQL syntax.
277. What is the purpose of SQL's LATERAL join?
- a) Correlate subqueries
- b) Flatten nested data
- c) Process arrays/JSON
- d) All of the above
Answer: D - Reference preceding FROM items in subqueries.
278. Which feature enables SQL queries on live APIs?
- a) RESTful table functions
- b) External data wrappers
- c) HTTP handlers
- d) All of the above
Answer: D - PostgreSQL FDWs, Oracle REST Data Services.
279. What is the purpose of SQL's QUALIFY clause?
- a) Filter window function results
- b) Validate data quality
- c) Test query syntax
- d) Check permissions
Answer: A - Snowflake/Teradata's post-aggregation filter.
280. Which database provides native vector similarity search?
- a) PostgreSQL with pgvector
- b) Oracle Vector
- c) SQL Server Semantic Search
- d) All of the above
Answer: D - AI/ML embedding-based retrieval.