Dbms lab 1
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The most common forms of normalization applied to databases are called the normal forms. Relations can be modified using the insert, delete, and update operators. It relates the two keys. For each department that has more than five employees, retrieve the department number and the number of its employees who are making more than Rs. All his orders must also be deleted. The remaining operators proposed by Codd involve special operations specific to relational databases: The selection, or restriction, operation retrieves tuples from a relation, limiting the results to only those that meet a specific criterion, i. Any set of tuples; a data report from the RDBMS in response to a query Relations or tables[ edit ] Main articles: Relation database and Table database A relation is defined as a set of tuples that have the same attributes. Find the name and numbers of all salesman who had more than one customer. Also, derived relations can be used as an abstraction layer. For example, in a database relating students, teachers, and classes. Constraints provide one method of implementing business rules in the database and support subsequent data use within the application layer. Delete a book in BOOK table. The first four operators were based on the traditional mathematical set operations : The union operator combines the tuples of two relations and removes all duplicate tuples from the result.
Demonstrate its working with a simple query. The use of efficient indexes on both primary and foreign keys can dramatically improve query performance.
Dbms lab manual doc
Compute the total number of male and female students in each semester and in each section. Add appropriate database constraints. The concept is described formally as: "For all tuples in the referencing relation projected over the referencing attributes, there must exist a tuple in the referenced relation projected over those same attributes such that the values in each of the referencing attributes match the corresponding values in the referenced attributes. Main article: data domain A domain describes the set of possible values for a given attribute, and can be considered a constraint on the value of the attribute. The character string "ABC", for instance, is not in the integer domain, but the integer value is. Stored procedures usually collect and customize common operations, like inserting a tuple into a relation , gathering statistical information about usage patterns, or encapsulating complex business logic and calculations. Constraints can apply to single attributes, to a tuple restricting combinations of attributes or to an entire relation. Main article: Index database An index is one way of providing quicker access to data. Derived relations are convenient in that they act as a single relation, even though they may grab information from several relations. In this type of join, two relations are connected by their common attributes. Relations can be modified using the insert, delete, and update operators. Sort the result by movie title. List all actors who acted in a movie before and also in a movie after use JOIN operation. It relates the two keys.
Also, derived relations can be used as an abstraction layer. Applications access data by specifying queries, which use operations such as select to identify tuples, project to identify attributes, and join to combine relations. Constraints[ edit ] Constraints make it possible to further restrict the domain of an attribute.
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Derived relations are convenient in that they act as a single relation, even though they may grab information from several relations. Frequently they are used as an application programming interface API for security or simplicity. In this type of join, two relations are connected by their common attributes. The intersection operator produces the set of tuples that two relations share in common. Main article: Unique key A primary key uniquely specifies a tuple within a table. Base and derived relations[ edit ] Main articles: Relvar and View database In a relational database, all data are stored and accessed via relations. Indexes can be created on any combination of attributes on a relation. Objects are typically physical objects or concepts.
Relational databases typically supply multiple indexing techniques, each of which is optimal for some combination of data distribution, relation size, and typical access pattern. These relations are sometimes called "derived relations".
Find the title of movies and number of stars for each movie that has at least one rating and find the highest number of stars that movie received. Main article: Unique key A primary key uniquely specifies a tuple within a table. Main article: Index database An index is one way of providing quicker access to data.
Sort the result by movie title. Mathematically, attaching a domain to an attribute means that any value for the attribute must be an element of the specified set.
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