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Found 6702 Articles for Database
8K+ Views
Query is a question or requesting information. Query language is a language which is used to retrieve information from a database.Query language is divided into two types −Procedural languageNon-procedural languageProcedural languageInformation is retrieved from the database by specifying the sequence of operations to be performed.For Example − Relational algebra.Structure Query language (SQL) is based on relational algebra.Relational algebra consists of a set of operations that take one or two relations as an input and produces a new relation as output.Types of Relational Algebra operationsThe different types of relational algebra operations are as follows −Select operationProject operationRename operationUnion operationIntersection operationDifference operationCartesian ... Read More
9K+ Views
Query is a question or requesting information. Query language is a language which is used to retrieve information from a database.Query language is divided into two types −Procedural languageNon-procedural languageProcedural languageInformation is retrieved from the database by specifying the sequence of operations to be performed.For Example − Relational algebra.Structure Query language (SQL) is based on relational algebra.Relational algebra consists of a set of operations that take one or two relations as an input and produces a new relation as output.Types of Relational Algebra operationsThe different types of relational algebra operations are as follows −Select operationProject operationRename operationUnion operationIntersection operationDifference operationCartesian ... Read More
11K+ Views
Query is a question or requesting information. Query language is a language which is used to retrieve information from a database.Query language is divided into two types −Procedural languageNon-procedural languageProcedural languageInformation is retrieved from the database by specifying the sequence of operations to be performed.For Example − Relational algebra.Structure Query language (SQL) is based on relational algebra.Relational algebra consists of a set of operations that take one or two relations as an input and produces a new relation as output.Types of Relational Algebra operationsThe different types of relational algebra operations are as follows −Select operationProject operationRename operationUnion operationIntersection operationDifference operationCartesian ... Read More
10K+ Views
Query is a question or requesting information. Query language is a language which is used to retrieve information from a database.Query language is divided into two types −Procedural languageNon-procedural languageProcedural languageInformation is retrieved from the database by specifying the sequence of operations to be performed.For Example − Relational algebra.Structure Query language (SQL) is based on relational algebra.Relational algebra consists of a set of operations that take one or two relations as an input and produces a new relation as output.Types of Relational Algebra operationsThe different types of relational algebra operations are as follows −Select operationProject operationRename operationUnion operationIntersection operationDifference operationCartesian ... Read More
7K+ Views
Query is a question or requesting information. Query language is a language which is used to retrieve information from a database.Query language is divided into two types −Procedural languageNon-procedural languageProcedural languageInformation is retrieved from the database by specifying the sequence of operations to be performed.For Example − Relational algebra.Structure Query language (SQL) is based on relational algebra.Relational algebra consists of a set of operations that take one or two relations as an input and produces a new relation as output.Types of Relational Algebra operationsThe different types of relational algebra operations are as follows −Select operationProject operationRename operationUnion operationIntersection operationDifference operationCartesian ... Read More
12K+ Views
Query is a question or requesting information. Query language is a language which is used to retrieve information from a database.Query language is divided into two types as follows −Procedural languageNon-procedural languageProcedural languageInformation is retrieved from the database by specifying the sequence of operations to be performed.For Example: Relational algebraStructure Query language (SQL) is based on relational algebra.Relational algebra consists of a set of operations that take one or two relations as an input and produces a new relation as output.The different types of relational algebra operations are −Select operationProject operationRename operationUnion operationIntersection operationDifference operationCartesian product operationJoin operationDivision operation.Select, project, ... Read More
6K+ Views
The different types which we need to consider while designing generalization and specialization in the Database Management System (DBMS) are as follows −Conditional definitionAttribute definedUser definedDisjoint definedOverlapping constraintCompleteness constraintLet us now understand them one by one.Conditional definitionCreate one database, and keep conditions on one attribute for example attendance. This type of constraint is defined on a single attribute which is further dividing an entity into two sub entity sets which will give information for the given attribute.ExampleGiven below is an example of the conditional definition database −Attribute definedThis refers to specifying conditions on more than one attribute.ExampleConsider a database for ... Read More
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Expression tree is also called a query tree. It demonstrates an evaluation plan.ExampleConsider an evaluation plan for the given query −Select name from customer, account where customer.name=account.name and account.balance>2000;There are two evaluation plans −Πcustomer.name(σcustomer.name=account.name^ account.balance>2000(customerXaccount)Πcustomer.name(σcustomer.name=account.name(customerXσ account.balance>2000(account)The expression trees for the above evaluation plans are as follows −Cost evaluator evaluates the cost of different evaluation plans and chooses the evaluation plan with lowest cost. Disk access time, CPU time, number of operations, number of tuples, size of tuples are considered for cost calculations.Read More
14K+ Views
Join dependency is a constraint which is similar to functional dependency or multivalued dependency. It is satisfied if and only if the relation concerned is the join of a certain number of projections. Such type of constraint is called join dependency.Let's consider a special class of join dependencies which help to capture data dependencies present in a hierarchical data structure.Example 1The above hierarchical organization informs regarding ward and patients currently admitted to a ward depend only on the hospital but not the facilities present in that hospital. Since hospitals have multiple wards, functional dependencies are not adequate to describe the ... Read More
3K+ Views
To understand why database management systems are necessary, let's look at a typical "file processing system" supported by conventional operating systems.ExampleTake an application in a saving bank. Saving accounts and customer records are kept in permanent system files.Application programs are written to manipulate files to perform some tasks like follows −Debit or credit an account.Add a new account.Find an account balance.Generate monthly statements.Development of the system proceeds as new application programs must be written as the need arises, new permanent files are created as required, but over a long period of time files may be in different formats and application ... Read More