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

what is mean by constraint?

Posted By :Narayanan     Posted Date :August 09, 2012    Points :40   Category :Sql Server 
constraint:
protect columns of the table from unwanted values.
NOT NULL, CHECK, UNIQUE, PRIMARY KEY, FOREIGN KEY are the types of contraints define in SQL Server.

You can also find related Interview Question to what is mean by constraint?  below: 

What is Check Constraint?

  
Check constraint specifies a condition that is enforced for each row of the table on which the constraint is defined. Once constraint is defined, insert or update to the data within the tables is checked against the defined constraint
(More...)

What is the difference between RULE and Check Constraint?

  
The major difference between rule and Check is reusability. Check constraint is associated with columns in a Table. So these can't be re-used. Rules are defined with in a database and can be applied to any number of columns. (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...)

What is NOT NULL Constraint?

  
A NOT NULL Constraint enforces that the column will not accept NULL values.The NOT NULL constraint are used to enforce domain integrity as the check constraint. (More...)

What are check constraint

  
? A CHECK constraint is used to limit the values that can be placed in a column.
? The check constraints are used to enforce domain integrity.
(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...)

What are NOT NULL Constraint

  
? A NOT NULL constraint enforces that the column will not accept null values.
? The not null constraints are used to enforce domain integrity, as the check constraints.
(More...)

what is not null constraint?


  
It enforces thata column will not accept null value. (More...)

Define check constraint?

  
It limits value that can be placed with in a column. (More...)

What is NOT NULL Constraint

  
A NOT NULL constraint enforces that the column will not accept null values. The not null constraints are used to enforce domain integrity, as the check constraints. (More...)

What is a constraint in SQL Server?

  
Constraint in SQL Server can be used to specify the limit on the data type of table. It can be specified while creating or altering the table statement. following constraints are SQL Server Query.
NOT NULL.
CHECK.
DEFAULT.
UNIQUE.
PRIMARY KEY.
FOREIGN KEY. (More...)

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