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Database:What is Unique key?

Posted By :shankey     Posted Date :July 28, 2011    Points :40   Category :Others 

Unique key also ensures the uniqueness of the column values but also it creates a non clustured index.

You can also find related Interview Question to Database:What is Unique key?  below: 

Database Concurrency in Sql Server.

When two or more user try to update same type of data in a table then Database Concurrency helps in this situation.

There are 2 types of Database Concurrency

Pessimistic: When one user try to change the data with pessimistic concurrency then a lock is placed on the data in a table so that another user cannot change data. when one user finishes then other user can able to change.

Optimistic: When two user works on the same data in a table and one change that data first then second user cannot change that same data becasue the which he have using is allready changed so he cannot do the change becasue change apply to another data that is changed by first user. (More...)

What is the .NET that allows the retrieval of data by a unique key?

HashTable is the .NET collection class that allows the retrieval of data by a unique key (More...)

What is a Database system?

The database and DBMS software together is called as Database system. (More...)

Unique Key constraint

1) UNIQUE constraints are to make sure that no duplicate values are entered in specific columns that do not participate in a primary key.
2) When you are placing an unique constraint it will automatically create Unique Index to maintain the integrity.
3) Unique Allows one Null value per column where as Primary key doesn't allow null values.
4) There is no limit on having number of unqiue constraints on a table.
5) Unique Key constraint can be referenced in Foreign Key Column. (More...)

Can SharePoint be linked to a SQL database?

This is possible via a custom application, but it not natively supported by SharePoint or SQLServer. (More...)

How many Files per database will accept?

32,767 files are the maximum number in SQL Server 2005 (More...)

Is it possible to create Cluster Index on Unique Key Column?

Unique key column by default creates a non-cluster index on the column. Primary key creates cluster index on the column. The only difference is Unique key column allows only one null value. So is it possible to have cluster index on Unique key column?

The answer is YES. Though Unique key allows null value but it still maintains the uniqueness of the column. (More...)

Name of the command to view the current amount of free (unallocated) space in the database in SQL Server?

Name of command is :sp_spaceused

This command displays the database_size in MB, and it's also shows unallocated space for the database. (More...)

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