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What is a centriade?
a centriade is a one with 609 nulls
What is relational algebra in DBMS explain with suitable example?
Relational algebraIn order to implement a DBMS, there must exist a set of rules which state how the database system will behave. For instance, somewhere in the DBMS must be a set of statements which indicate than when someone inserts data into a row of a relation, it has the effect which the user expects. One way to specify this is to use words to write an `essay' as to how the DBMS will operate, but words tend to be imprecise and open to interpretation. Instead, relational databases are more usually defined using Relational Algebra.Relational Algebra is :the formal description of how a relational database operatesan interface to the data stored in the database itselfthe mathematics which underpin SQL operationsOperators in relational algebra are not necessarily the same as SQL operators, even if they have the same name. For example, the SELECT statement exists in SQL, and also exists in relational algebra. These two uses of SELECT are not the same. The DBMS must take whatever SQL statements the user types in and translate them into relational algebra operations before applying them to the database.TerminologyRelation - a set of tuples.Tuple - a collection of attributes which describe some real world entity.Attribute - a real world role played by a named domain.Domain - a set of atomic values.Set - a mathematical definition for a collection of objects which contains no duplicates.Operators - WriteINSERT - provides a list of attribute values for a new tuple in a relation. This operator is the same as SQL.DELETE - provides a condition on the attributes of a relation to determine which tuple(s) to remove from the relation. This operator is the same as SQL.MODIFY - changes the values of one or more attributes in one or more tuples of a relation, as identified by a condition operating on the attributes of the relation. This is equivalent to SQL UPDATE.Operators - RetrievalThere are two groups of operations: Mathematical set theory based relations: UNION, INTERSECTION, DIFFERENCE, and CARTESIAN PRODUCT.Special database operations: SELECT (not the same as SQL SELECT), PROJECT, and JOIN.Relational SELECTSELECT is used to obtain a subset of the tuples of a relation that satisfy a select condition. For example, find all employees born after 1st Jan 1950: SELECTdob '01/JAN/1950'(employee)Relational PROJECTThe PROJECT operation is used to select a subset of the attributes of a relation by specifying the names of the required attributes. For example, to get a list of all employees surnames and employee numbers: PROJECTsurname,empno(employee)SELECT and PROJECTSELECT and PROJECT can be combined together. For example, to get a list of employee numbers for employees in department number 1:Figure : Mapping select and project Set Operations - semanticsConsider two relations R and S. UNION of R and S the union of two relations is a relation that includes all the tuples that are either in R or in S or in both R and S. Duplicate tuples are eliminated.INTERSECTION of R and S the intersection of R and S is a relation that includes all tuples that are both in R and S.DIFFERENCE of R and S the difference of R and S is the relation that contains all the tuples that are in R but that are not in S.SET Operations - requirementsFor set operations to function correctly the relations R and S must be union compatible. Two relations are union compatible if they have the same number of attributesthe domain of each attribute in column order is the same in both R and S.UNION ExampleFigure : UNION INTERSECTION ExampleFigure : Intersection DIFFERENCE ExampleFigure : DIFFERENCE CARTESIAN PRODUCTThe Cartesian Product is also an operator which works on two sets. It is sometimes called the CROSS PRODUCT or CROSS JOIN. It combines the tuples of one relation with all the tuples of the other relation.CARTESIAN PRODUCT exampleFigure : CARTESIAN PRODUCT JOIN OperatorJOIN is used to combine related tuples from two relations: In its simplest form the JOIN operator is just the cross product of the two relations.As the join becomes more complex, tuples are removed within the cross product to make the result of the join more meaningful.JOIN allows you to evaluate a join condition between the attributes of the relations on which the join is undertaken.The notation used is R JOINjoin condition SJOIN ExampleFigure : JOIN Natural JoinInvariably the JOIN involves an equality test, and thus is often described as an equi-join. Such joins result in two attributes in the resulting relation having exactly the same value. A `natural join' will remove the duplicate attribute(s). In most systems a natural join will require that the attributes have the same name to identify the attribute(s) to be used in the join. This may require a renaming mechanism.If you do use natural joins make sure that the relations do not have two attributes with the same name by accident.OUTER JOINsNotice that much of the data is lost when applying a join to two relations. In some cases this lost data might hold useful information. An outer join retains the information that would have been lost from the tables, replacing missing data with nulls. There are three forms of the outer join, depending on which data is to be kept.LEFT OUTER JOIN - keep data from the left-hand tableRIGHT OUTER JOIN - keep data from the right-hand tableFULL OUTER JOIN - keep data from both tablesOUTER JOIN example 1Figure : OUTER JOIN (left/right) OUTER JOIN example 2Figure : OUTER JOIN (full)
Do Group functions include nulls in calculations?
FALSE
What is Nulls partner?
Zero
What is a centriade?
a centriade is a one with 609 nulls
Length of a null string is supposed to be 1?
A null has no length... I dont know java or c but in sql and vb there are functions to convert nulls isnull(some_field,' ') would return either the field, or a space if its null
What is the use of nulls in a database?
Usually there is no use of nulls but in some case there might be some use. Like consider a case a persons address has been changed but the new address is not known. In this case it is prefer to left the field null instead of wrong address.
Are there any reported hauntings in Polk County Arkansas?
yes they are.... rich mt. old water plant, nulls hill, billys b in potter
When does the Michelangelo virus take effect every year?
On March 6, if the PC is an AT or a PS/2, the virus overwrites the first one hundred sectors of the hard disk with nulls.
What are the names of the foster parents Dave pelzer had?
Micheal and Joanne Nulls Lily and Rudy Catanze (second) Harold and Alice Turnbought (last) Jody and Vera Jones John and Linda Walsh Aunt Mary (First)
What are some locations offering pick and pull services for auto parts?
There are several places that offer pick and pull services for autos. There are many Pick Nulls throughout the United States. There are also other companies that offer the same service.
What 5 letter word is there with L as number 4 letter?
agile, bully, calls, dells, eagle, falls, gulls, hills, inkle, jello, knoll, ladle, mulls, nulls, orale, prole, quill, rolls, sells, tells, utile, voile, whole, yells, zeals
What does michelangelo virus do also refer to reason the virus has this name?
Essentially, the Michelangelo virus overwrites the first hundred sectors of the hard disk with nulls and moves the original master boot record. This can cause a loss of information, as well as the inability to boot your operating system. It gets its name from the fact that infected computers are affected if booted up on March 6th, the birthday of the renaissance painter of the same name.
How do you get the code for gold in frugooscape?
No. There isn't a real code for money. if you type in ::pickup 1004 1 that means 1 10,000, or 1 null. so it actually isn't money at all it's just a null. so if you type in ::pickup 1004 999999999 that would b3 999M Nulls. there is a code for money it is ::pickup 0995 999999999 = 999m if you whant more code email me at lukestearn@hotmail.co.UK 0lukestarn0
