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Consider the relations described below: PHYSICIAN (regno, name, telno, city)PATIENT (pname, street, city) VISIT (pname, regno, date_of_visit, fee) Where the regno and pname identify the physician and the patient uniquely corresponding. Express queries (i) to (iii) in SQL.(i) Get the name and regno of physicians who are in Delhi.(ii) Find out the name and city of patient(s) who visited a physician on 31 August 2004.(iii) Get the name of the physician and the total number of patients who have visited her.(iv) What does the subsequent SQL query answer SELECT DISTINCT nameFROM PHYSICIAN PWHERE NOT EXISTS( SELECT *FROM VISITWHERE regno = p.regno )
(i) Select name, regno from PHYSICIAN where city = ‘Delhi'; (ii) Select pname, city from PATIENT,VISIT where PATIENT.pname=VISIT.pname and date_of_visit = '31-Aug-04'; (iii) select name, count(*) from PHYSICIAN, VISIT where PHYSICIAN.regno = VISIT.regno group by Physician . regno; (iv) This will provide the name of physicians who have not visited any patient.
Write short note on Data models? Data models: A data model is an abstract model which elaborates how data is represented and accessed. The term data model has two commonly ac
Operator Precedence The basic operators used in SQL are * / - + Operators of the similar priority are evaluated From Left to right Parentheses are used to force priorit
Self-Join: In a self join a table is joined with itself. Let consider the following sample partial data of EMP table EMPNO ENAME MGRID
Dirty Reads: T10 reads a value which is updated by T9. This update has not been committed and T9 aborts. T9 T10 Value of x old value = 200
Type of views : Simple views and Difficult Views Feature Simple Views Complex Views Number of tables One
what are the type of the database
What are stored and derived attributes? Stored attributes: The attributes keeps in a data base are known as stored attributes. Derived attributes: The attributes that are de
Explain three main attributes of data.
What are the basic objects of the data dictionary? Tables Domains Data elements Structures Foreign Keys
Define a relation ? Relation - A relations is a named two-dimensional table of data. Mathematically, a relation can be described as a subset of the cartesian product of a lis
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