Interview Questions and Answers - ADO.NET & SQL Server

What is the role of the DataReader class in ADO.NET connections?

It returns a read-only, forward-only rowset from the data source. A DataReader provides fast access when a forward-only sequential read is needed.

What are advantages and disadvantages of Microsoft-provided data provider classes in ADO.NET?

SQLServer.NET data provider is high-speed and robust, but requires SQL Server license purchased from Microsoft. OLE-DB.NET is universal for accessing other sources, like Oracle, DB2, Microsoft Access and Informix. OLE-DB.NET is a .NET layer on top of the OLE layer, so its not as fastest and efficient as SqlServer.NET.

What is the wildcard character in SQL?

Lets say you want to query database with LIKE for all employees whose name starts with La. The wildcard character is %, the proper query with LIKE would involve ‘La%.

Explain ACID rule of thumb for transactions.

A transaction must be:

  1. Atomic - it is one unit of work and does not dependent on previous and following transactions.
  2. Consistent - data is either committed or roll back, no “in-between― case where something has been updated and something hasnt.
  3. Isolated - no transaction sees the intermediate results of the current transaction).
  4. Durable - the values persist if the data had been committed even if the system crashes right after.

What connections does Microsoft SQL Server support?

Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and password).

Between Windows Authentication and SQL Server Authentication, which one is trusted and which one is untrusted?

Windows Authentication is trusted because the username and password are checked with the Active Directory, the SQL Server authentication is untrusted, since SQL Server is the only verifier participating in the transaction.

What does the Initial Catalog parameter define in the connection string?

The database name to connect to.

What does the Dispose method do with the connection object?

Deletes it from the memory.
To Do : answer better. The current answer is not entirely correct.

What is a pre-requisite for connection pooling?

Multiple processes must agree that they will share the same connection, where every parameter is the same, including the security settings. The connection string must be identical.


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