the basic constraints that can be specified when you create a table in SQL Database Management Systems 10CS54 VTU notes 4 Marks Jun July2014June 2016

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the basic constraints that can be specified, when you create a table in SQL. Database Management Systems - 10CS54 VTU notes 4 Marks (Jun / July2014/June 2016)

 Explain with an example ,


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Tuples in the referencing relation R1 have attributes FK (called foreign key attributes) that reference the primary key attributes PK of the referenced relation R2. A tuple t1 in R1 is said to reference a tuple t2 in R2 if t1[FK] = t2[PK] A referential integrity constraint can be displayed in a relational database schema as a directed arc from R1.FK to R2. 

• Entity integrity constraint -The entity integrity constraint states that no primary key P Q R 10 a 5 15 b 8 25 a 6 VTUlive.com 31 value can be null. This is because the primary key value is used to identify individual tuples in a relation: having null values for the primary keys implies that we cannot identify some tuples. 
Key constraints and entity constraints are specified on individual relations.
 • Referential integrity constraint - The referential integrity constraint is specified between two relations and is used to maintain the consistency among tuples of the two relations. A tuple in one relation that refers to another relation must refer to an existing tuple in that relation. 
• Foreign key is a set of attributes of one relation R1 whose values are required to match values of some candidate key of some relation R2 . For example, the value of attribute DNO in every EMPLOYEE tuple must match the DNUMBER value of some tuple in the DEPARTMENT relation. 

Nikhil-bharadwaj

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