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What is a foreign key, and what is it used for?
A foreign key is used to establish relationships between relations in the relational model. Technically, a foreign key is a column (or columns) appearing in one relation that is (are) the primary key of another table. Although there might be exceptions, the values in the foreign key columns usually must correspond to values existing in the set of primary key values. This correspondence necessity is created in a database using a referential integrity constraint on the foreign key.
What is the difference between serial and sequential files? How searching is applied on both? Ans: A serial file is one where the records have been stored in the order where
Consider the following frequency counts of some itemsets in a transaction database r : freq({A}, r) = 0.405 freq({B}, r) = 0.510 freq({C}, r) = 0.303 freq({A
Differentiate between natural join and outer join? Natural join is a binary operator which is written as (R * S) where as R and S are relations. The output of the natural join
Question: Using the data model express the following queries in SQL. (a) Create the Table named "Cinema" and make the cinema_code to be the primary key of the relation and
The result of the UNION operation between R1 and R2 is a relation that includes? The result of the operation between R1 and R2 includes all the tuples of R1 and R2 which have c
Draw and explain the three level architecture of the database system? A DBMS gives three levels of data is said to follow three-level architecture. The trget of the three-schem
Discuss The difference between drop table R and delete from R. DROP TABLE command deletes all the records with the table definition. This command will automatically committed
in an organization several projects are undertaken. Each project can employ one or more employees. Each employee can work on one or more projects. Each project is undertaken on the
Process of Adjustment of inheritance During object design, inheritance is readjusted by rearranging classes and operations, and abstracting common behaviour.
Explain outer join? Outer Join - If there are any values in one table which do not have corresponding value(s) in the other, in an equi-join which will not be chosen. Such ro
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