.NET Tutorials, Forums, Interview Questions And Answers
Welcome :Guest
 
Sign In
Register
 
Win Surprise Gifts!!!
Congratulations!!!


Top 5 Contributors of the Month
david stephan

Home >> Interview Question >> Sql Server >> Post New Question Subscribe to Interview Questions

How you will create a UNIQUE Constraint when the table is already created?

Posted By :Syed Shakeer Hussain     Posted Date :November 29, 2009    Points :10   Category :Sql Server 
ALTER TABLE table_name
ADD UNIQUE (Column_Name)

You can also find related Interview Question to How you will create a UNIQUE Constraint when the table is already created?  below: 

What command is used to create a table by copying the structure of another table?

  
CREATE TABLE .. AS SELECT command

Explanation :

To copy only the structure, the WHERE clause of the SELECT command should contain a FALSE statement as in the following.
CREATE TABLE NEWTABLE AS SELECT * FROM EXISTINGTABLE WHERE 1=2;
If the WHERE condition is true, then all the rows or rows satisfying the condition will be copied to the new table. (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...)

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...)

How to create a Unique Indix?

  
Create UNIQUE INDEX Index_Name
On dbo.TABLENAME(COLUMN_NAME) (More...)

Which command is used to create a table by copying the structure of another table?

  
CREATE TABLE .. AS SELECT command
Example:-
CREATE TABLE AS SELECT*FROM WHERE 1=2; (More...)

Would the select query below fetch any records?



create table #testvm (ID int)

select * from sysobjects where name = '#testvm'

drop table #testvm

  
No..

Since temp tables are created in tempdb, and use a random name, the query will not work.

If you used a query like this, you would see your table:

select * from tempdb..sysobjects where name like '#testvm%' (More...)

How do we create table from another table in sql?

  

CREATE TABLE new_table
AS (SELECT * FROM old_table);
(More...)

What are UNIQUE KEY constraint

  
? It enforces the uniqueness of the values in a set of columns, so no duplicate values are entered.
? The unique key constraints are used to enforce entity integrity as the primary key constraints.
(More...)

Database should be created as a SINGLE_USER state Whenever you create a new Database. What should you do ?

  
1. Normally, when we create a new database, All the properties will be inherited from the Model database.

2. So, Just change the Model database's State to SINGLE_USER.

3. Now onwards, The new database will be created as SINGLE_USER state. (More...)

Quick Links For Interview Questions Categories:
ASP.Net Windows Application   .NET Framework   C#   VB.Net   ADO.Net  
Sql Server   SharePoint   Silverlight   OOPs   JQuery   JavaScript/VBScript
Biztalk Patten/Practices .IIS WCF WPF WWF
Networking Aptitude Others   All      

Find questions, FAQ's and their answers related to .NET, C#, Vb.Net, Sql Server and many more.

 
Now you can find lots of .NET, C#, Vb.Net, SQL Server,Windows, ASP.Net related Questions and their Answers here at www.dotnetspark.com. Our aim is to help you pass your certification Exams (MCP, MCSD, MCAD etc.,) with flying scores and get good name in your company.

So, Start looking our Interview Question section daily and improve your .NET Skills. You can also help others by posting Interview Questions and their Answers in this section.


Hall of Fame    Twitter   Terms of Service    Privacy Policy    Contact Us    Archives   Tell A Friend