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What are check constraint

Posted By :Karthikeyan Anbarasan     Posted Date :January 07, 2011    Points :15   Category :Sql Server 
? 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.

You can also find related Interview Question to What are check 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

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...)

Define check constraint?

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

How can we check that some changes have been made to dataset since it was loaded?


The changes made to the dataset can be tracked using the GetChanges and HasChanges methods.
The GetChanges returns dataset which are changed since it was loaded or since Acceptchanges was executed.

The HasChanges property indicates if any changes were made to the dataset since it was loaded or if acceptchanges method was executed.

The RejectChanges can be used to revert thee changes made to the dataset since it was loaded


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...)

How can check the Oracle version information from the command prompt?

Version information is stored in a table called v$version. In this table we can find version information on Oracle, PL/SQL, etc.

To retrieve the version information for Oracle, we can execute the following SQL statement:

select * from v$version
where banner like 'Oracle%'; (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.

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.

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