Common SQL server questions. Part 1.

  1. How do you use transactions? - 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.
  2. Describe the difference between truncate and delete – . Truncate means to simply empty out a table(Id starts from zero). 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.
  3. 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.
  4. What is Identity? - Identity (or AutoNumber) is a column that automatically generates numeric values.
  5. What is cursor? - Cursor is a database object used by applications to manipulate data in a set on a row-by-row basis, instead of the typical SQL commands that operate on all the rows in the set at one time.
  6. What’s the difference between a primary key and a unique key? – Both primary key and unique enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where are unique creates a nonclustered index by default. Another major difference is that, primary key doesn’t allow NULLs, but unique key allows one NULL only.
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