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In a relation, tuples are not inserted in any definite order. Ordering of tuples is not defined as a part of a relation definition. Though, records may be structured later according to some attribute value in the storage systems. For instance, records in PERSON table may be structured according to PERSON_ID. Such organisation or data depends on the requirement of the underlying database application. Though, for the purpose of display we may get them displayed in the sorted order of age. The following table is sorted by age. It is also worth states here that relational model does not permit duplicate tuples
PERSON
PERSON_ID NAME AGE ADDRESS
2 Sharad Gupta 33 Pocket 2, Mayur Vihar.
1 Sanjay Prasad 35 b-4,Modi Nagar
3 Vibhu Datt 36 c-2, New Delhi
Super Keys, Candidate Keys and Primary Keys for the Relations
As discussed in the last section ordering of relations does not matter and all tuples in a relation are unique. Though, can we uniquely recognize a tuple in a relation? Let us talk about the concepts of keys that are primarily used for the purpose as above.
what is definition hierarchical data model
Consider the table student and list names of students in the departments other than maths and computer. SELECT std_name FRM student WHERE dept_name NOT IN (‘Maths','Computer);
Write an sql statement to find what is the percentage of home policies which are from the state of Arizona out of all Home policies by Policy Value.
What is the need for triggers? Triggers are useful mechanisms for alerting humans or for starting particular tasks automatically when particular conditions are met.
CAN SOMEONE HELP ME WITH ENTITY DIAGRAMS IN FIRST NORMAL FORM?
Timestamps For Read operations: If TS (T) If TS (T) >= W-timestamp (Q), then the transaction T is trying to read a value of data item Q which has been written and committed
External failure : A failure can also result because of an external cause, such as earthquakes, fire, floods, etc. The database must be duly backed up to avoid troubles occurring d
In E-R diagram how generalization is represented? in E-R diagram generalization is represented by Triangle shape.
construct a b-tree for the following set of key values 2,3,5,7,11,17,19,23,29,31.assume that the tree is initial empty and the values are added in ascending order
What do you mean by Correlated subquery? Subqueries, or nested queries, are used to bring back a set of rows to be used by the parent query. Depending on how the subquery is writ
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