CLASS 11 12 JEE NEET
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*Answer*
A primary key is a special relational database table column (or combination of columns) designated to uniquely identify each table record. A primary key is used as a unique identifier to quickly parse data within the table. A table cannot have more than one primary key.
*Answer*
127) The given query will fetch all columns and records ( rows) from the movies table.
128) It get all the columns from Customers table.
*Answer*
a) Select Salary +1000 from Emp;
b) Select Emp_id, Salary – 500 from Emp;
c) Select Ename, Salary * 3 from Emp;
d) Select Emp_id, Ename, Salary/2 from Emp;
e) Select Emp_id, Ename from Emp;
Write the queries for the following table : Emp
Emp_id Ename Salary
1 Suman 20000
2 Sanjay 32000
3 Ravi 30000
a. Display the salary of all the employees after incrementing by Rs 1000.
b. Display the Employee id and salary of all the employees after decreasing by Rs 500.
c. Display the Name and salary of all the employees after incrementing it as thrice the amount of present salary.
d. Display the Employee id, Name and salary of all the employees after decrementing it as half the amount of present salary.
e. Display the Employee id and Name of all the employees.
In Hierarchical data model, relationship between table and data is defined in parent child structure. In this structure data are arranged in the form of a tree structure. This model supports one-to-one and one-to-many relationships. On the other hand, network model arrange data in graph structure.
