Services
Technology Web App Development Mobile App Development Windows App Development Database Development UI/UX Development Cloud Development SEO Digital Marketing Guest Posting Content Writing Artificial Intelligence Data Science ERP Development CRM Development CMS Development LMS Development Business Listing Blockchain Technology Startup Promotion AI Tools Integration
Products
Data Converter Cleaner TUC - Unit Converter Import Export Survey Manager Tweet Controller
Developer
Article Blog Forum Interview Beginner News Startup Quiz
Users
Career
Apply Job Internship
Pricing
Login Sign Up Get a Quote

interview

home / developersection / interviews / what is a "constraint"?
Ask Question
Pushpendra Singh
Pushpendra Singh

Other

Message

2 Answers

Amit Singh
Amit Singh 09 Nov 2010
Report Abuse

A constraint is an expression that specifies the semantics of an element, and it must always be true.

Constraint is a restriction on table.There are two types of

constraints 1.ananymous constraint and 2.named

constraint.under named and ananymous constraints there are

1.primary key constraint

2.foreign key constraint

3. not null constraint

4. check constraint

5. unique constraint.



Pushpendra Singh
Pushpendra Singh 01 Nov 2010
Report Abuse
A constraint allows you to apply simple referential integrity checks to a table. There are four primary types of constraints that are currently supported by SQL Server: PRIMARY/UNIQUE - enforces uniqueness of a particular table column. DEFAULT - specifies a default value for a column in case an insert operation does not provide one. FOREIGN KEY - validates that every value in a column exists in a column of another table. CHECK - checks that every value stored in a column is in some specified list. Each type of constraint performs a specific type of action. Default is not a constraint. NOT NULL is one more constraint which does not allow values in the specific column to be null. And also it the only constraint which is not a table level constraint.
advertising