Let’s prepare sample data for SQL practice.
Sample Table – Worker
| WORKER_ID |
FIRST_NAME |
LAST_NAME |
SALARY |
JOINING_DATE |
DEPARTMENT |
| 001 |
Monika |
Arora |
100000 |
2021-02-20 09:00:00 |
HR |
| 002 |
Niharika |
Verma |
80000 |
2021-06-11 09:00:00 |
Admin |
Sample Table – Bonus
| WORKER_REF_ID |
BONUS_DATE |
BONUS_AMOUNT |
| 1 |
2023-02-20 00:00:00 |
5000 |
| 2 |
2023-06-11 00:00:00 |
3000 |
Sample Table – Title
| WORKER_REF_ID |
WORKER_TITLE |
AFFECTED_FROM |
| 1 |
Manager |
2023-02-20 00:00:00 |
| 2 |
Executive |
2023-06-11 00:00:00 |
Query – Worker Table
CREATE TABLE Worker (
WORKER_ID INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
FIRST_NAME CHAR(25),
LAST_NAME CHAR(25),
SALARY INT(15),
JOINING_DATE DATETIME,
DEPARTMENT CHAR(25)
);
INSERT INTO Worker
(WORKER_ID, FIRST_NAME, LAST_NAME, SALARY, JOINING_DATE, DEPARTMENT) VALUES
(001, 'Monika', 'Arora', 100000, '21-02-20 09.00.00', 'HR'),
(002, 'Niharika', 'Verma', 80000, '21-06-11 09.00.00', 'Admin'),
(003, 'Vishal', 'Singhal', 300000, '21-02-20 09.00.00', 'HR'),
(004, 'Amitabh', 'Singh', 500000, '21-02-20 09.00.00', 'Admin'),
(005, 'Vivek', 'Bhati', 500000, '21-06-11 09.00.00', 'Admin'),
(006, 'Vipul', 'Diwan', 200000, '21-06-11 09.00.00', 'Account'),
(007, 'Satish', 'Kumar', 75000, '21-01-20 09.00.00', 'Account'),
(008, 'Geetika', 'Chauhan', 90000, '21-04-11 09.00.00', 'Admin');
Query – Bonus Table
CREATE TABLE Bonus (
WORKER_REF_ID INT,
BONUS_AMOUNT INT(10),
BONUS_DATE DATETIME,
FOREIGN KEY (WORKER_REF_ID)
REFERENCES Worker(WORKER_ID)
ON DELETE CASCADE
);
INSERT INTO Bonus
(WORKER_REF_ID, BONUS_AMOUNT, BONUS_DATE) VALUES
(001, 5000, '23-02-20'),
(002, 3000, '23-06-11'),
(003, 4000, '23-02-20'),
(001, 4500, '23-02-20'),
(002, 3500, '23-06-11');
Query – Title Table
CREATE TABLE Title (
WORKER_REF_ID INT,
WORKER_TITLE CHAR(25),
AFFECTED_FROM DATETIME,
FOREIGN KEY (WORKER_REF_ID)
REFERENCES Worker(WORKER_ID)
ON DELETE CASCADE
);
INSERT INTO Title
(WORKER_REF_ID, WORKER_TITLE, AFFECTED_FROM) VALUES
(001, 'Manager', '2023-02-20 00:00:00'),
(002, 'Executive', '2023-06-11 00:00:00'),
(008, 'Executive', '2023-06-11 00:00:00'),
(005, 'Manager', '2023-06-11 00:00:00'),
(004, 'Asst. Manager', '2023-06-11 00:00:00'),
(007, 'Executive', '2023-06-11 00:00:00'),
(006, 'Lead', '2023-06-11 00:00:00'),
(003, 'Lead', '2023-06-11 00:00:00');
SQL query interview questions:
Q-1. Write an SQL query to fetch “FIRST_NAME” from the Worker table using the alias name
.
Select FIRST_NAME AS WORKER_NAME from Worker;
Q-2. Write an SQL query to fetch “FIRST_NAME” from the Worker table in upper case.
Select upper(FIRST_NAME) from Worker;
Q-3. Write an SQL query to fetch unique values of DEPARTMENT from the Worker table.
Select distinct DEPARTMENT from Worker;
Q-4. Write an SQL query to print the first three characters of FIRST_NAME from the Worker table.
Select substring(FIRST_NAME,1,3) from Worker;
Q-5. Write an SQL query to find the position of the alphabet (‘a’) in the first name column ‘Amitabh’ from
the Worker table.
Select INSTR(FIRST_NAME, BINARY'a') from Worker where FIRST_NAME = 'Amitabh';
Q-6. Write an SQL query to print the FIRST_NAME from the Worker table after removing white
spaces from the right side.
Select RTRIM(FIRST_NAME) from Worker;
Q-7. Write an SQL query to print the DEPARTMENT from the Worker table after removing white
spaces from the left side.
Select LTRIM(DEPARTMENT) from Worker;
Q-8. Write an SQL query that fetches the unique values of DEPARTMENT from the Worker table and
prints its length.
Select distinct length(DEPARTMENT) from Worker;
Q-9. Write an SQL query to print the FIRST_NAME from the Worker table after replacing ‘a’ with
‘A’.
Select REPLACE(FIRST_NAME,'a','A') from Worker;
Q-10. Write an SQL query to print the FIRST_NAME and LAST_NAME from the Worker table into a
single column COMPLETE_NAME. A space char should separate them.
Select CONCAT(FIRST_NAME, ' ', LAST_NAME) AS 'COMPLETE_NAME' from Worker;
Q-11. Write an SQL query to print all Worker details from the Worker table order by FIRST_NAME
Ascending.
Select * from Worker order by FIRST_NAME asc;
Q-12. Write an SQL query to print all Worker details from the Worker table order by FIRST_NAME
Ascending and DEPARTMENT Descending.
Select * from Worker order by FIRST_NAME asc,DEPARTMENT desc;
Q-13. Write an SQL query to print details for Workers with the first names “Vipul” and “Satish”
from the Worker table.
Select * from Worker where FIRST_NAME in ('Vipul','Satish');
Q-14. Write an SQL query to print details of workers excluding first names, “Vipul” and
“Satish” from the Worker table.
Select * from Worker where FIRST_NAME not in ('Vipul','Satish');
Q-15. Write an SQL query to print details of Workers with DEPARTMENT name as “Admin”.
Select * from Worker where DEPARTMENT like 'Admin%';
Q-16. Write an SQL query to print details of the Workers whose FIRST_NAME contains ‘a’.
Select * from Worker where FIRST_NAME like '%a%';
Q-17. Write an SQL query to print details of the Workers whose FIRST_NAME ends with ‘a’.
Select * from Worker where FIRST_NAME like '%a';
Q-18. Write an SQL query to print details of the Workers whose FIRST_NAME ends with ‘h’ and
contains six alphabets.
Select * from Worker where FIRST_NAME like '_____h';
Q-19. Write an SQL query to print details of the Workers whose SALARY lies between 100000 and
500000.
Select * from Worker where SALARY between 100000 and 500000;
Q-20. Write an SQL query to print details of the Workers who joined in Feb 2021.
Select * from Worker where year(JOINING_DATE) = 2021 and month(JOINING_DATE) = 2;
Q-21. Write an SQL query to fetch the count of employees working in the department ‘Admin’.
SELECT COUNT(*) FROM worker WHERE DEPARTMENT = 'Admin';
Q-22. Write an SQL query to fetch worker names with salaries >= 50000 and <= 100000.
SELECT CONCAT(FIRST_NAME, ' ' , LAST_NAME) As Worker_Name, Salary FROM worker WHERE WORKER_ID IN (SELECT WORKER_ID FROM worker WHERE Salary BETWEEN 50000 AND 100000);
Q-23. Write an SQL query to fetch the number of workers for each department in descending order.
SELECT DEPARTMENT, count(WORKER_ID) No_Of_Workers FROM worker GROUP BY DEPARTMENT ORDER BY No_Of_Workers DESC;
Q-24. Write an SQL query to print details of the Workers who
are also Managers.
SELECT DISTINCT W.FIRST_NAME, T.WORKER_TITLE FROM Worker W INNER JOIN Title T ON W.WORKER_ID=T.WORKER_REF_ID AND T.WORKER_TITLE in ('Manager');
Q-25. Write an SQL query to fetch duplicate
records having matching data in some fields of a table.
SELECT WORKER_TITLE, AFFECTED_FROM, COUNT(*) FROM Title GROUP BY WORKER_TITLE, AFFECTED_FROM HAVING COUNT(*)> 1;
Q-26. Write an SQL query to show only odd rows from a table.
SELECT * FROM Worker WHERE MOD (WORKER_ID, 2) <> 0;
Q-27. Write an SQL query to show only even rows from a table.
SELECT * FROM Worker WHERE MOD (WORKER_ID, 2) = 0;
Q-28. Write an SQL query to clone a new table from another table.
The general query to clone a table with data is:
SELECT * INTO WorkerClone FROM Worker;
The general way to clone a table without information is:
SELECT * INTO WorkerClone FROM Worker WHERE 1 = 0;
An alternate way to clone a table (for MySQL) without data is:
CREATE TABLE WorkerClone LIKE Worker;
Q-29. Write an SQL query to fetch intersecting records of two tables.
(SELECT * FROM Worker) INTERSECT (SELECT * FROM WorkerClone);
Q-30. Write an SQL query to show records from one table that another table does not have.
SELECT * FROM Worker MINUS SELECT * FROM Title;
Q-31. Write an SQL query to show the current date and time.
The following MySQL query returns the current date:
SELECT CURDATE();
Whereas the following MySQL query returns the current date and time:
SELECT NOW();
Here is a SQL Server query that returns the current date and time:
SELECT getdate();
Find this Oracle query that also returns the current date and time:
SELECT SYSDATE FROM DUAL;
Q-32. Write an SQL query to show the top n (say 10) records of a table.
MySQL query to return the top n records using the LIMIT method:
SELECT * FROM Worker ORDER BY Salary DESC LIMIT 10;
SQL Server query to return the top n records using the TOP command:
SELECT TOP 10 * FROM Worker ORDER BY Salary DESC;
Oracle query to return the top n records with the help of ROWNUM:
SELECT * FROM (SELECT * FROM Worker ORDER BY Salary DESC) WHERE ROWNUM <= 10;
Q-33. Write an SQL query to determine the nth (say n=5) highest salary from a table.
SELECT Salary FROM Worker ORDER BY Salary DESC LIMIT n-1,1;
Q-34. Write an SQL query to determine the 5th highest salary without using the TOP or limit
method.
The following query is using the correlated subquery to return the 5th highest salary:
SELECT Salary FROM Worker W1 WHERE 4=( SELECT COUNT( DISTINCT ( W2.Salary ) ) FROM Worker W2 WHERE W2.Salary>=W1.Salary);
Use the following generic method to find the nth highest salary without using TOP or limit.
SELECT Salary FROM Worker W1 WHERE n-1 = (SELECT COUNT( DISTINCT ( W2.Salary ))FROM Worker W2 WHERE W2.Salary >= W1.Salary);
Q-35. Write an SQL query to fetch the list of employees with the same salary.
Select distinct W.WORKER_ID, W.FIRST_NAME, W.Salary from Worker W, Worker W1 where W.Salary = W1.Salary and W.WORKER_ID != W1.WORKER_ID;
Q-36. Write an SQL query to show the second-highest salary from a table.
Select max(Salary) from Worker where Salary not in (Select max(Salary) from Worker);
Q-37. Write an SQL query to show one row twice in the results from a table.
Select FIRST_NAME, DEPARTMENT from worker W where W.DEPARTMENT='HR'union all Select FIRST_NAME, DEPARTMENT from Worker W1 where W1.DEPARTMENT='HR';
Q-38. Write an SQL query to fetch intersecting records of two tables.
(SELECT * FROM Worker)INTERSECT (SELECT * FROM WorkerClone);
Q-39. Write an SQL query to fetch the first 50% of records from a table.
SELECT * FROM WORKER WHERE WORKER_ID <= (SELECT count(WORKER_ID)/2 from Worker);
Q-40. Write an SQL query to fetch the departments that have less than five people in them.
SELECT DEPARTMENT, COUNT(WORKER_ID) as 'Number of Workers' FROM Worker GROUP BY DEPARTMENT HAVING COUNT(WORKER_ID) < 5;
Q-41. Write an SQL query to show all departments along with the number of people in there.
SELECT DEPARTMENT,COUNT(DEPARTMENT) as 'Number of Workers' FROM Worker GROUP BY DEPARTMENT;
Q-42. Write an SQL query to show the last record from a table.
Select * from Worker where WORKER_ID=(SELECT max(WORKER_ID) from Worker);
Q-43. Write an SQL query to fetch the first row of a table.
Select * from Worker where WORKER_ID=(SELECT min(WORKER_ID) from Worker);
Q-44. Write an SQL query to fetch the last five records from a table.
SELECT * FROM Worker WHERE WORKER_ID <=5 UNION SELECT * FROM (SELECT * FROM Worker W order by W.WORKER_ID DESC) AS W1 WHERE W1.WORKER_ID <=5;
Q-45. Write an SQL query to print the names of employees having the highest salary in each department.
SELECT t.DEPARTMENT,t.FIRST_NAME,t.Salary from(SELECT max(Salary) as TotalSalary,DEPARTMENT from Worker group by DEPARTMENT) as TempNew Inner Join Worker t on TempNew.DEPARTMENT=t.DEPARTMENT and TempNew.TotalSalary=t.Salary;
Q-46.Write an SQL query to fetch three max salaries from a table.
SELECT distinct Salary from worker a WHERE 3>= (SELECT count(distinct Salary) from worker b WHERE a.Salary <= b.Salary) order by a.Salary desc;
Q-47. Write an SQL query to fetch three min salaries from a table.
SELECT distinct Salary from worker a WHERE 3>=(SELECT count(distinct Salary) from worker b WHERE a.Salary >= b.Salary) order by a.Salary desc;
Q-48. Write an SQL query to fetch nth max salaries from a table.
SELECT distinct Salary from worker a WHERE n >= (SELECT count(distinct Salary) from worker b WHERE a.Salary <= b.Salary) order by a.Salary desc;
Q-49. Write an SQL query to fetch departments along with the total salaries paid
for each of them.
SELECT DEPARTMENT, sum(Salary) from worker group by DEPARTMENT;
-50. Write an SQL query to fetch the names of workers who earn the highest salary.
SELECT FIRST_NAME, SALARY from Worker WHERE SALARY=(SELECT max(SALARY) from Worker);
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