Found 1719 Articles for Big Data Analytics

Cost-based optimization is expensive. Heuristics are used to reduce the number of choices that must be made in a cost-based approach.RulesHeuristic optimization transforms the expression-tree by using a set of rules which improve the performance. These rules are as follows −Perform the SELECTION process foremost in the query. This should be the first action for any SQL table. By doing so, we can decrease the number of records required in the query, rather than using all the tables during the query.Perform all the projection as soon as achievable in the query. Somewhat like a selection but this method helps in ... Read More

SQL queries are decomposed into query blocks. One query block contains a single SELECT-FROM-WHERE expression, as well as GROUP BY and HAVING clause (if any). Nested queries are split into separate query blocks.ExampleConsider an example given below −Select lastname, firstname from employee where salary>(select max(salary) from employee where deptname =CSE ; C=(select max(salary) from employee where deptname=CSE); // inner block Select lastname, firstname from employee where salary>c; //outer blockWhere C represents the result returned from the inner block.The relation algebra for the inner block is Ģmax(salary) (σdname=CSE(employee))The relation algebra for the outer blocks is Πlastname, firstname(σsalary>c(employee))The query optimizer would then ... Read More

Join operation combines the relation R1 and R2 with respect to a condition. It is denoted by ⋈.The different types of join operation are as follows −Theta joinNatural joinOuter join − It is further classified into following types −Left outer join.Right outer join.Full outer join.Theta joinIf we join R1 and R2 other than the equal to condition then it is called theta join/ non-equi join.ExampleConsider R1 tableRegNoBranchSection1CSEA2ECEB3CIVILA4ITB5ITATable R2NameRegNoBhanu2Priya4R1 ⋈ R2 with condition R1.regno > R2.regnoRegNoBranchSectionNameRegno3CIVILABhanu24ITBBhanu25ITABhanu25ITBPriya4In the join operation, we select those rows from the cartesian product where R1.regno>R2.regno.Join operation = select operation + cartesian product operationNatural joinIf we join R1 ... Read More

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

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

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

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

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

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

Query is a question or requesting information. Query language is a language which is used to retrieve information from a database.Relational algebraIt is a procedural query language. It gives a step-by-step process to obtain the result of the query. It uses operators to perform queries.Relational algebra can be depicted as follows −Algebraic OperationsThe different algebraic operations in the DBMS are as follows −Let us understand the relational algebra operations in DBMS.Select operationIt displays the records that satisfy a condition. It is denoted by sigma (σ). It is a horizontal subset of the original relation.Syntaxσcondition(table name)Projection operationIt displays the specific column ... Read More