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Define check constraint?
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Posted Date :
July 31, 2011
It limits value that can be placed with in a column.
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Define check constraint?
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.
How you will create a CHECK Constraint when the table is already created
ALTER TABLE table_name
ADD CHECK (P_Id>0)
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.
Define namespace in C++ ?
It is a feature in c++ to minimize name collisions in the global name space. This namespace keyword assigns a distinct name to a library that allows other libraries to use the same identifier names without creating any name collisions. Furthermore, the compiler uses the namespace signature for differentiating the definitions.
Define precondition and post-condition to a member function.
A precondition is a condition that must be true on entry to a member function. A class is used correctly if preconditions are never false. An operation is not responsible for doing anything sensible if its precondition fails to hold.
For example, the interface invariants of stack class say nothing about pushing yet another element on a stack that is already full. We say that isful() is a precondition of the push operation.
A post-condition is a condition that must be true on exit from a member function if the precondition was valid on entry to that function. A class is implemented correctly if post-conditions are never false.
For example, after pushing an element on the stack, we know that isempty() must necessarily hold. This is a post-condition of the push operation.
Define the "integrity rules"
There are two Integrity rules.
1.Entity Integrity: States that "Primary key cannot have NULL value"
2.Referential Integrity: States that "Foreign Key can be either a NULL value or should be Primary Key value of other relation.
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.
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.
How you will create a UNIQUE Constraint when the table is already created?
ALTER TABLE table_name
ADD UNIQUE (Column_Name)
Name the method in VB.NET used to define a controls color?
How to define a button USING XAML?
To define a button in WPD using XAML use the following syntax,
element specifies the use of the Button class.
To define abstract class in VB which keyword is used?
MustInherit keyword is used to create an abstract class in VB.
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