List of top Database Management Systems Questions on SQL

Consider the relational database with the following four schemas and their respective instances: \[ \text{Student(sNo, sName, dNo)} \text{       }\text{Dept(dNo, dName)} \\ \text{Course(cNo, cName, dNo)} \text{         } \text{Register(sNo, cNo)} \] 

SQL Query: 

SELECT * FROM Student AS S WHERE NOT EXIST
 (SELECT cNo FROM Course WHERE dNo = “D01”
	EXCEPT 
 SELECT cNo FROM Register WHERE sNo = S.sNo) 

The number of rows returned by the above SQL query is___________.

The relation scheme given below is used to store information about the employees of a company, where empId is the key and deptId indicates the department to which the employee is assigned. Each employee is assigned to exactly one department. 
\[ \text{emp}(\text{empId},\ \text{name},\ \text{gender},\ \text{salary},\ \text{deptId}) \] 

Consider the following SQL query: 

select deptId, count(*) 
from emp 
where gender = "female" and salary > (select avg(salary) from emp) 
group by deptId; 

The above query gives, for each department in the company, the number of female employees whose salary is greater than the average salary of