0 votes 0 votes how many tables are required? Databases databases er-to-relational virtual-gate-test-series + – aditi19 asked May 28, 2019 • edited Aug 18, 2019 by Lakshman Bhaiya aditi19 1.4k views answer comment Share Follow See all 26 Comments See all 26 26 Comments reply srestha commented May 30, 2019 reply Follow Share 3 tables and if more merge we can do it only 2 tables. Ans given?? I think 3 tables is ans 0 votes 0 votes srestha commented May 30, 2019 reply Follow Share chk this, same type :https://gateoverflow.in/312661/made-easy-test-series-databases-tables 0 votes 0 votes aditi19 commented May 31, 2019 reply Follow Share ans is 5 tables 0 votes 0 votes srestha commented May 31, 2019 reply Follow Share @aditi19 Can u give explaination, why?? 0 votes 0 votes aditi19 commented Jun 1, 2019 reply Follow Share @ushamya has given th explanation 0 votes 0 votes srestha commented Jun 1, 2019 reply Follow Share Her explanation is not clear , not clearly visible too I m sure 5 is not correct 0 votes 0 votes aditi19 commented Jun 1, 2019 reply Follow Share Test, Patient and Doctor are strong entities, so each will be represented with a table. so we have 3 tables A patient can be checked by multiple doctors and a doctor can check multiple patients. so this is m:n relationship. Checks relationship will be represented with a table with primary keys of both doctor and patient table. [for m:n relationships we require a separate table which consists primary keys of both the tables] Similarly the relationship 'performed by' is m:n. so it requires a separate table The relation Test-log b/w Patient and Test is 1:n with total participation on Test side. hence, the relationship 'performed by' need not be represented with another table. The Test relation will contain PK of the Patient relation [one-to--many relationships that are total on many side do not require extra table] 1 votes 1 votes srestha commented Jun 1, 2019 reply Follow Share @aditi19 yes correct. But can we not merge total participation in 1 table?? 0 votes 0 votes aditi19 commented Jun 1, 2019 reply Follow Share here the total participation is on one side. so we can't 0 votes 0 votes srestha commented Jun 1, 2019 reply Follow Share Total participation on $n$ side. Then we cannot merge?? why?? which book u got it? 0 votes 0 votes aditi19 commented Jun 1, 2019 reply Follow Share How will u merge it? pls explain @srestha 0 votes 0 votes aditi19 commented Jun 1, 2019 reply Follow Share answer me this there are two entities Employee(empno, ename) here empno is primary key Insurance(ino, amount, maturity date) here ino is primary key the relationship b/w them is 'has' i.e. an employee has insurance, The cardinality of the relationship is 1:n i.e. one employee can have several insurances. and the relationship on 'n' side(Endurance) is total it means every Insurance no. must be held by some employee Instead of having a separate table for the relationship 'has' we create the table Insurance(ino, amount, maturity date, empno). correct? so now empno becomes foreign key in the table Insurance. it points to the primary key of table Employee if you merge the table Employee and Insurance then the primary keys of Employee table will be repeated(as one employee can hold more than one insurance). This is violation of entity integrity constraint so w/o violating this constraint how can we merge the two tables? 0 votes 0 votes ushamya commented Jun 1, 2019 reply Follow Share @srestha Please refer: https://www.geeksforgeeks.org/mapping-from-er-model-to-relational-model/ https://gateoverflow.in/218954/what-an-interesting-dbms-question 0 votes 0 votes srestha commented Jun 1, 2019 reply Follow Share 2) if relationship is many to one and many side entity is only partially participation you can merge in one table ===> redundancy and transitive dependencies get but not partial functional dependencies. because of pk(new table)=pk(E1) 3) if relationship is many to one and one side entity is only partially participation you can't merge in one table ===> 2 tables required these lines are supporting ur ans @ushamya right?? 0 votes 0 votes srestha commented Jun 1, 2019 reply Follow Share @aditi19 Do u mean multivalued dependency?? But in this image , no multivalued dependency is there. right?? Moreover can u tell, then how u merge m:n participations, if both side has a total participation?? 0 votes 0 votes ushamya commented Jun 1, 2019 reply Follow Share @srestha Yes and one more is: if relationship is many to many and both entities are partially participation you can't merge ===> require 3 tables 1 votes 1 votes aditi19 commented Jun 1, 2019 reply Follow Share @srestha no where I've mentioned MVD. MVD concept is different 0 votes 0 votes srestha commented Jun 1, 2019 reply Follow Share what about m:n and both total participation?? How to merge in 1 table?? 0 votes 0 votes srestha commented Jun 1, 2019 reply Follow Share (as one employee can hold more than one insurance) @aditi19 this condition for MVD 0 votes 0 votes ushamya commented Jun 2, 2019 reply Follow Share @srestha For many to many, entities in both sides can be merged if we have total participation on both sides. 0 votes 0 votes aditi19 commented Jun 2, 2019 reply Follow Share (as one employee can hold more than one insurance) this is not MVD. your MVD concept is wrong. clear it from some standard book. MVD can exists when there is at least three attributes. Eg- R(A, B, C). A multi-determines B, B multi-determines C. this is MVD simply A having multiple values of B is not MVD 0 votes 0 votes srestha commented Jun 2, 2019 reply Follow Share @aditi19 it should be MVA , instead of MVD I mean multivalued attribute, ok now?? 0 votes 0 votes aditi19 commented Jun 2, 2019 reply Follow Share yes 0 votes 0 votes srestha commented Jun 5, 2019 reply Follow Share yes 5 answer. But is really total participation makes any changes? 0 votes 0 votes ushamya commented Jun 5, 2019 reply Follow Share @srestha Yes, participation constraints make changes. 0 votes 0 votes eshita1997 commented Dec 20, 2020 reply Follow Share 5 tables are required. 0 votes 0 votes Please log in or register to add a comment.
5 votes 5 votes 5 tables are required . ushamya answered May 29, 2019 ushamya comment Share Follow See all 0 reply Please log in or register to add a comment.