Answer 2. One to one , One to many , Many to one and Many to many.
Question 4. Consider a database of students and the courses they take. Discuss the normalization required on the following table and its need.
Answer 4. StudentCoursemappingTable(stud_id,course_id) ,CourseMasterTable(course_id,course_fee)
Answer 5. It is used to check similarity of strings
Answer 6. It is used to check if a value belongs to a set of values.
Question 7. Entity- relationship model is a special type of _________.
Answer 7. Object based logical model.
Question 8. What is the difference between inner join and outer join?
Answer 8. An inner join between two or more tables is the cartesian product that satisfies the join condition in the WHERE clause. Whereas outer join retrives those values which are matched and unmatched by WHERE clause.
Question 9. Define 2nd normal form?
Answer 9. A relation is said to be 2nd normal form if it is infirst normal form and every non-prime attribute is fully funtionally dependent on a key.
Answer 10. No, to do that we have to alter the table and drop constraints.
- Grant: to grant access to a user on a database object(table) toperform only certain operations.
- Revoke : to take back the access.
- Commit: to mark the end of a transaction. writes into the data file.
- Rollback:- to go back to the original consistant state
Question 12. List the aggregate functions?
Answer 12. sum, avg, min, max,varience, count, stddev
Question 13. List the problems of concurrency
- Loss of update
- Dirty read
- Incorrect summary
- Phantom record
Question 14. What is the difference between the usage of the aggregate function ‘COUNT’ when we say, (i)select count(*) from and select count(field_name) from ?
Answer 14. In case of (i), Count(*) will count the total number of rows including those with NULL in some columns.
In case of (ii), Count(col_name) will count those rows where the value of col_name is not null.
Question 15. What is the difference between DROP and DELETE commands?
DROP – Is a DDL Command and once it is executed, the structure and data in the table is permanently lost.
DELETE – Is a DML Command and delete will remove the records or rows in a table based on specified conditions.
Question 16. What is Cardinality ?
Answer 16. Cardinality – The cardinality of a relationship is NOT the count of number of records in a table but it is the way the relationship exists in the schema. For instance, a 1:n cardinality refers to the fact that for every 1 entry in the first table, the second table can have n entries.
Question 17. Difference between UNION & UNION ALL