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This constraint shows that the key attribute value in each tuple must be unique, i.e., no two tuples have the similar value for the key attribute. This is because the value of the primary key is used to recognize the tuples in the relation.
Example: If A is the key attribute in the following relation R than A1, A2 and A3 must be unique.
A
B
A1
B1
A3
B2
A2
Example: In relation PERSON, PERSON_ID is primary key so PERSON_ID cannot be given as the similar for two persons.
Integrity Constraint
There are two kinds of integrity constraints:
Complete replication: It implies maintaining of a whole copy of the database at every site. Thus, the reliability & availability and performance for query response are maximized.
Security: In a centralised system, access to the data can be simply controlled. Though, in a distributed DBMS not only does access to replicated data have to be controlled in many
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Query Processor The query language processor is responsible for taking query language statements or shifting them from the English-like syntax of the query language to a form
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Record based Logical Models: Use records as the key data representation components Examples: Relational Model: It shows data as well as relationship between data in the form
(a) What is a Sub-Query? (b) What is the difference between a scalar sub-query and a tabular sub-query? (c) Write an equivalent SQL statement to get the Name of Product wh
Write an sql statement to find what is the percentage of home policies which are from the state of Arizona out of all Home policies by Policy Value.
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