Top 10 Sql Questions

  1. What are DMVs? – Dynamic Management Views (DMVs), are functions that give you information on the state of the server. DMVs, for the most part, are used to monitor the health of a server. They really just give you a snapshot of what’s going on inside the server. They let you monitor the health of a server instance, troubleshoot major problems and tune the server to increase performance.
  2. Define a temp table – In a nutshell, a temp table is a temporary storage structure. What does that mean? Basically, you can use a temp table to store data temporarily so you can manipulate and change it before it reaches its destination format.
  3. What’s the difference between a local  temp table and a global temp table? – Local tables are accessible to a current user connected to the server. These tables disappear once the user has disconnected from the server. Global temp tables, on the other hand, are available to all users regardless of the connection. These tables stay active until all the global connections are closed.
  4. How do you use transactions? – In general, there are three types of transactions that you can use in the SQL Server environment: BEGIN TRANSACTION, ROLL BACK TRANSACTION and COMMIT TRANSACTION. The gist behind deploying transactions is that they allow you to group multiple SQL commands into a single unit. From there, each transaction begins with a certain task, and ends when all the tasks within the transaction are complete. BEGIN TRANSACTION gets the ball rolling. ROLLBACK TRANSACTION functions a lot like an “undo” command, and COMMIT TRANSACTION completes all of the tasks within that transaction.
  5. What’s the difference between a clustered and a non-clustered index? – A clustered index directly affects the way tabled data is stored on a specific disk. This means that when a clustered index is used, data is stored in sequential rows based on the index column value. This is why a table can only contain a single clustered index. Non-clustered indexes directly affect the way physical data is stored and managed within SQL Server.
  6. What are DBCC commands? – In very basic terms the Database Consistency Checker (DBCC) is used to aid in server maintenance. DBCC commands, many of which are completely undocumented, provide a set of commands that let you perform routing maintenance, status and validation checks. The most common DBCC commands are: DBCC CHECKALLOC (Lets you check disk allocation); DBCC OPENTRAN (Lets you check any open transactions); and DBCC HELP (shows a list of available DBCC commands to aid your server maintenance processes).
  7. Describe the difference between truncate and delete – The difference between these two processes is fairly simple. Truncate means to simply empty out a table. On the other hand, the delete command lets you delete entire rows from within a table, but not all of the data within that table.
  8. What is a view? – A view is simply a virtual table that is made up of elements of multiple physical or “real” tables. Views are most commonly used to join multiple tables together, or control access to any tables existing in background server processes.
  9. What is a Query Execution Plan? – SQL Server has several built-in tools that optimize how queries are executed within their databases. A query execution plan is exactly what it sounds like – a snapshot of how the optimizing tools will execute and deploy specific queries within the database. This service helps you troubleshoot problems with jobs that don’t necessarily execute perfectly.
  10. What is the default port number for SQL Server? – While this is kind of a softball question – if you know anything about SQL Server you should at least know the basic configuration options – it’s an important one to nail in the interview. Basically, when SQL Server is enabled the server instant listens to the TCP port 1433.

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