'Employee' with structure as ID, name, Address, Phone, Deptno
'Department' with structure as Deptno, Dname
_____ is used to represent the relationship between two relations Employee and Department.
Understanding Database Relationships: Employee and Department Tables
The question asks about the specific database concept used to link two different tables, specifically the 'Employee' table and the 'Department' table. We are given the structures of these tables:
- Employee Table: Contains columns like ID, name, Address, Phone, and Deptno.
- Department Table: Contains columns like Deptno and Dname.
The common column, 'Deptno', present in both tables is the key to establishing a connection or relationship between an employee and their respective department.
Database Keys Explained
Let's look at the different types of keys mentioned in the options to understand why one is correct:
- Primary Key: A column (or set of columns) that uniquely identifies each record within a table. For example, 'ID' in the Employee table is likely a primary key. 'Deptno' might be the primary key in the Department table.
- Candidate Key: Any column or set of columns that *could* serve as a primary key because it uniquely identifies records. Both 'ID' and potentially 'Deptno' (if unique in Employee) could be candidate keys for the Employee table.
- Alternate Key: A candidate key that was not chosen as the primary key. If 'Deptno' uniquely identified employees but 'ID' was chosen as the primary key, then 'Deptno' would be an alternate key.
- Foreign Key: A column (or set of columns) in one table that refers to the primary key (or another unique key) in another table. It creates a link between the two tables and ensures referential integrity (meaning you can't have an employee assigned to a department that doesn't exist).
Identifying the Linking Mechanism
In this scenario, the 'Deptno' column in the 'Employee' table points to the 'Deptno' in the 'Department' table. This is exactly the function of a Foreign Key. The 'Deptno' in the Employee table is referencing the primary key ('Deptno') of the Department table, thereby representing the relationship: each employee belongs to a specific department.
Therefore, the Foreign Key is used to represent the relationship between the Employee and Department relations.
Important Questions from Miscellaneous
A stone is thrown horizontally from the top of a 20 m high building with a speed of 12 m/s. It hits the ground at a distance R from the building. Taking g = 10 m/s2 and neglecting air resistance will give :
A sphere of volume V is made of a material with lower density than water. While on Earth, it floats on water with its volume f1V (f1 < 1) submerged. On the other hand, on a spaceship accelerating with acceleration a < g (g is the acceleration due to gravity on Earth) in outer space, its submerged volume in water is f2V. Then:
A railway wagon (open at the top) of mass M1 is moving with speed v1 along a straight track. As a result of rain, after some time it gets partially filled with water so that the mass of the wagon becomes M2 and speed becomes v2. Taking the rain to be falling vertically and the water stationery inside the wagon, the relation between the two speeds v1 and v2 is :
Consider the following statements:
1. Distance between the longitudes becomes zero on North Pole and South Pole.
2. Distance between the longitudes is maximum on the Equator.
3. Number of longitudes is more than number of latitudes.
Which of the statements given above is/are correct?
One block of 2⋅0 kg mass is placed on top of another block of 3⋅0 kg mass. The coefficient of static friction between the two blocks is 0⋅2. The bottom block is pulled with a horizontal force F such that both the blocks move together without slipping. Taking acceleration due to gravity as 10 m/s2, the maximum value of the frictional force is :
