Are you preparing for an SQL Server interview? Whether you’re a beginner or an experienced database administrator, understanding SQL Server concepts is essential. This guide provides a detailed collection of frequently asked SQL Server interview questions and answers to help you succeed in your next technical interview.
1. Log Shipping vs. Database Mirroring
- Log Shipping:
- One primary database with multiple secondary databases.
- Asynchronous synchronization.
- No automatic failover.
- Suitable for read-only secondary servers.
- Database Mirroring:
- One principal database and one mirror database.
- Supports both synchronous and asynchronous modes.
- Automatic failover (only in high-safety mode with a witness).
- Ensures high availability.
2. Best Practices for SQL Server Patching
- Always test patches in a non-production environment.
- Take full database and transaction log backups before patching.
- Schedule patching during non-peak hours.
- Use a rolling update approach for minimal downtime.
- Monitor system performance after applying patches.
- Maintain rollback documentation in case of failure.
3. SQL Server System Databases
- Master: Stores system-level information such as logins and configurations.
- Model: Template for new databases.
- MSDB: Used for SQL Server Agent jobs, backups, and alerts.
- TempDB: Stores temporary objects and query processing data.
- Resource: A hidden read-only database storing system objects.
4. SQL Server Backup Types
- Full Backup: Captures the entire database.
- Differential Backup: Captures changes since the last full backup.
- Transaction Log Backup: Backs up transaction logs for point-in-time recovery.
- Copy-Only Backup: A full backup that does not affect the differential base.
- File/Filegroup Backup: Backs up specific database files.
- Mirror Backup: Creates an exact copy of the backup file.
5. Isolation Levels in SQL Server
| Isolation Level | Dirty Reads | Non-Repeatable Reads | Phantom Reads |
|---|---|---|---|
| Read Uncommitted | Yes | Yes | Yes |
| Read Committed | No | Yes | Yes |
| Repeatable Read | No | No | Yes |
| Serializable | No | No | No |
| Snapshot | No | No | No |
6. Always On Availability Groups
- Provides high availability and disaster recovery with multiple replicas.
- Supports synchronous (zero data loss) and asynchronous (better performance) commit modes.
- Allows automatic failover, read-only secondaries, and backup offloading.
7. New Features in SQL Server 2022
- Azure Synapse Link: Seamless integration with Azure Synapse.
- Contained Availability Groups: Simplifies failover configurations.
- Intelligent Query Processing Enhancements: Optimized query performance.
- SQL Ledger: Blockchain-like ledger for tamper-proof data integrity.
- Data Virtualization: Access external data without replication.
8. SQL Server Lock Types
- Shared (S): Allows multiple read operations.
- Exclusive (X): Blocks all other access.
- Update (U): Prevents deadlocks between read/update transactions.
- Intent (IS, IX, IU): Indicates intent to lock at a higher level.
- Schema Modification (Sch-M): Used for DDL changes.
- Bulk Update (BU): Used during bulk inserts.
9. SQL Server Memory Allocation
- Uses Min Server Memory and Max Server Memory settings.
- The Buffer Pool stores cached data pages.
- The Plan Cache optimizes queries with execution plans.
- Worker Threads use memory for query processing.
- Resource Governor allocates memory among workloads.
10. Common SQL Server DMV and DBCC Commands
| Category | DMV / DBCC Command | Description |
| Session Monitoring | sys.dm_exec_sessions | Active sessions |
| sys.dm_exec_requests | Running queries | |
| Locking & Blocking | sys.dm_tran_locks | Lock details |
| sys.dm_os_waiting_tasks | Blocking queries | |
| Index & Performance | sys.dm_db_index_usage_stats | Index usage stats |
| sys.dm_db_index_physical_stats | Index fragmentation | |
| DBCC Maintenance | DBCC CHECKDB | Database consistency check |
| DBCC CHECKTABLE | Table consistency check | |
| DBCC Performance | DBCC SHOW_STATISTICS | Index statistics |
| DBCC DBREINDEX | Rebuild index | |
| DBCC Monitoring | DBCC SQLPERF(logspace) | Log space usage |
| DBCC FREEPROCCACHE | Clear cache |
Final Thoughts
Understanding SQL Server’s fundamental concepts, best practices, and troubleshooting techniques can help database administrators and developers improve system performance, enhance security, and ensure high availability. Mastering these topics will also prepare you well for SQL Server interviews and real-world challenges.
Search results for “Interview Questions“