What is difference between DELETE & TRUNCATE commands?

Which TCP/IP port does SQL Server run on? How can it be changed?

SQL Server runs on port 1433. It can be changed from the Network Utility TCP/IP properties -> Port number, both on client and the server.

What are the difference between clustered and a non-clustered index? 

 A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages.

A non clustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk. The leaf node of a non clustered index does not consist of the data pages. Instead, the leaf nodes contain index rows.

What are the different index configurations a table can have?

A table can have one of the following index configurations:

• No indexes
• A clustered index
• A clustered index and many non-clustered indexes
•  A non-clustered index
• Many non-clustered indexes

What are different types of Collation Sensitivity?

Case sensitivity – A and a, B and b, etc.

Accent sensitivity – a and á, o and ó, etc.

Kana Sensitivity – When Japanese kana characters Hiragana and Katakana are treated differently, it is called Kana sensitive.

Width sensitivity – A single-byte character (half-width) and the same character represented as a double-byte character (full-width) are treated differently than it is width sensitive.

What is OLTP (Online Transaction Processing)?

In OLTP – online transaction processing systems relational database design use the discipline of data modeling and generally follow the Codd rules of data normalization in order to ensure absolute data integrity. Using these rules complex information is broken down into its most simple structures (a table) where all of the individual atomic level elements relate to each other and satisfy the normalization rules.

What’s the difference between a primary key and a unique key?

Both primary key and unique key enforces 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.

What is difference between DELETE & TRUNCATE commands?

Delete command removes the rows from a table based on the condition that we provide with a WHERE clause. Truncate will actually remove all the rows from a table and there will be no data in the table after we run the truncate command.

TRUNCATE

• TRUNCATE is faster and uses fewer system and transaction log resources than DELETE.
• TRUNCATE removes the data by deallocating the data pages used to store the table’s data, and only the page deallocations are recorded in the transaction log.
• TRUNCATE removes all rows from a table, but the table structure, its columns, constraints, indexes and so on, remains. The counter used by an identity for new rows is reset to the seed for the column.
• You cannot use TRUNCATE TABLE on a table referenced by a FOREIGN KEY constraint. Because TRUNCATE TABLE is not logged, it cannot activate a trigger.
• TRUNCATE cannot be rolled back.
• TRUNCATE is DDL Command.
• TRUNCATE Resets identity of the table.

DELETE

• DELETE removes rows one at a time and records an entry in the transaction log for each deleted row.
• If you want to retain the identity counter, use DELETE instead. If you want to remove table definition and its data, use the DROP TABLE statement.
• DELETE Can be used with or without a WHERE clause.
• DELETE Activates Triggers.
• DELETE can be rolled back.
• DELETE is DML Command.
• DELETE does not reset identity of the table.

DROP

• The DROP command removes a table from the database.
• All the tables' rows, indexes and privileges will also be removed.
• No DML triggers will be fired.
• The operation cannot be rolled back.
• DROP and TRUNCATE are DDL commands, whereas DELETE is a DML command.
• DELETE operations can be rolled back (undone), while DROP and TRUNCATE operations cannot be rolled back.

Difference between Close() and Dispose() Method

The basic difference between Close() and Dispose() is, when a Close() method is called, any managed resource can be temporarily closed and can be opened once again. It means that, with the same object the resource can be reopened or used. Whereas Dispose () method permanently removes any resource unmanaged from memory for cleanup and the resource no longer exists for any further processing.

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