18.

A  join operation is used to combine rows from two or more tables based on a related column between them. It is one of the fundamental operations used in relational databases for querying and retrieving data from multiple tables simultaneously.

Ans:

                 Select e.emp_name,e.province,e.city,b.branch,b.salary from Employee e

                  Left join  Branch  b  on e.emp_name=b.emp_name;

 

                Select e.emp_name,e.province,e.city,b.branch,b.salary from Employee e

               Right join  Branch  b  on e.emp_name=b.emp_name;

 

21.

a.Select R_Name ,R_address from Resturant

Where R_ID IN (Select R_id from works where Wshift=’day’);

 

b.Select r.R_Name,r.R_address from Resturant r

Join Works w on r.R_ID=W.R_ID

AND  Wshift=’day’;

 

c. Select C_name from Cook where C_specilization=’Italian’;

Select count(*),Wshift from Works_At 

Where Wshift=’night’;

 

d. Select avg(salary) from Cook;

Select R_Name,B_ID from Resturant

Where R_ID IN(Select R_ID from Branch where B_ID IN(select B_ID from Branch where revenue>15000));

 

 e.Select r.R_Name,b.B_ID from Resturant r

 Join Branch b on r.R_ID=b.R_ID

 Where b.revenue>15000;

            

22.

Normalization is a critical concept in various fields, including databases, statistics, and machine learning. It involves organizing data in a structured manner to eliminate redundancy and dependency, ensuring efficient storage, retrieval, and analysis. Here are some key reasons why normalization is important: