SQL Interview Questions

Curated questions for beginner, experienced, and scenario-based interviews. Use the filter to jump to what you need.

Showing 246 of 246

Scenario-Based SQL Interview Questions

Hands-on problems with sample solutions and SQL snippets. Try writing a solution before expanding the provided answer.

What is the syntax for SELECT statement in SQL?
The syntax for SELECT statement in SQL is as follows:
```
SELECT column1, column2, ... 
FROM table_name;
```
What is the use of the WHERE clause in SQL?
The WHERE clause in SQL is used to filter rows from a table based on specific conditions.
How to find the second highest salary of an employee in a table?
The following query can be used to find the second highest salary of an employee in a table:
```
SELECT MAX(salary) 
FROM employee 
WHERE salary NOT IN (SELECT MAX(salary) 
FROM employee);
```
What is the difference between INNER JOIN and LEFT JOIN in SQL?
INNER JOIN returns only the rows from both tables where there is a match. LEFT JOIN returns all the rows from the left table and matching rows from the right table. If there is no match, NULL values will be displayed for the right table's columns.
How to find the total number of rows in a table?
The following query can be used to find the total number of rows in a table:
```
SELECT COUNT(*) 
FROM table_name;
```
How to find the average salary of employees in a table?
The following query can be used to find the average salary of employees in a table:
```
SELECT AVG(salary) 
FROM employee;
```
How to find the minimum and maximum salary of employees in a table?
The following query can be used to find the minimum and maximum salary of employees in a table:
```
SELECT MIN(salary), MAX(salary) 
FROM employee;
```
How to sort the data in a table in ascending or descending order?
The following query can be used to sort the data in a table in ascending or descending order:
```
SELECT * 
FROM table_name ORDER BY column_name;  
SELECT * 
FROM table_name ORDER BY column_name DESC;
```
How to group the data in a table based on a column?
The following query can be used to group the data in a table based on a column:
```
SELECT column1, SUM(column2) 
FROM table_name GROUP BY column1;
```

How to update data in a table?

The following query can be used to update data in a table:

UPDATE table_name SET column1 = value1, column2 = value2, ... 
WHERE some_column = some_value;

How to delete data from a table?
The following query can be used to delete data from a table:
```
DELETE 
FROM table_name 
WHERE some_column = some_value;
```

How to insert data into a table?

The following query can be used to insert data into a table:

INSERT INTO table_name (column1, column2, column3, ...) VALUES (value1, value2, value3, ...);

What is the use of the LIKE operator in SQL?
The LIKE operator in SQL is used to search for a specified pattern in a column. The following query can be used to search for a specified pattern in a column:
```
SELECT * 
FROM table_name 
WHERE column_name LIKE 'pattern';
```
What is the use of the IN operator in SQL?
The IN operator in SQL is used to specify multiple values in a WHERE clause. The following query can be used to search for multiple values in a column:
```
SELECT * 
FROM table_name 
WHERE column_name IN (value1, value2, value3, ...);
```
What is the use of the DISTINCT keyword in SQL?
The DISTINCT keyword in SQL is used to return unique values from a SELECT statement. The following query can be used to return unique values from a column:
```
SELECT DISTINCT column_name 
FROM table_name;
```
What is the use of the BETWEEN operator in SQL?
The BETWEEN operator in SQL is used to select values within a specified range. The following query can be used to select values within a specified range:
```
SELECT * 
FROM table_name 
WHERE column_name BETWEEN value1 AND value2;
```
What is the use of the ALIAS in SQL?
The ALIAS in SQL is used to give a temporary name to a column or table. The following query can be used to give a temporary name to a column:
```
SELECT column_name AS alias_name 
FROM table_name; The following query can be used to give a temporary name to a table: SELECT column_name 
FROM table_name AS alias_name;
```

How to join multiple tables in SQL?

The following query can be used to join multiple tables in SQL:

SELECT column1, column2, ... 
FROM table1 JOIN table2 ON table1.column = table2.column JOIN table3 ON table2.column = table3.column ...;

What is the use of the UNION operator in SQL?
The UNION operator in SQL is used to combine the result-set of two or more SELECT statements into a single result-set. The following query can be used to combine the result-set of two SELECT statements into a single result-set:
```
SELECT column_name 
FROM table1 
UNION 
SELECT column_name 
FROM table2;
```
What is the use of the GROUP BY clause in SQL?
The GROUP BY clause in SQL is used to group rows that have the same values into summary rows, like finding the total count for each group. The following query can be used to group rows based on the values in a column:
```
SELECT column_name, aggregate_function(column_name) 
FROM table_name GROUP BY column_name;
```
What is the use of the HAVING clause in SQL?
The HAVING clause in SQL is used to restrict the groups of returned rows from the GROUP BY clause. The following query can be used to restrict the groups of returned rows based on aggregate functions:
```
SELECT column_name, aggregate_function(column_name) 
FROM table_name GROUP BY column_name HAVING aggregate_function(column_name) operator value;
```
What is the use of the LIMIT clause in SQL?
The LIMIT clause in SQL is used to specify the number of records to return in a SELECT statement. The following query can be used to return a specified number of records:
```
SELECT column_name 
FROM table_name LIMIT number_of_records;
```
What is the use of the INNER JOIN in SQL?
The INNER JOIN in SQL is used to combine rows from two or more tables based on the values of the joined columns, and only returns the rows that have matching values in both tables. The following query can be used to combine rows from two tables based on the values of the joined columns:
```
SELECT column1, column2, ... 
FROM table1 
INNER JOIN table2 ON table1.column = table2.column;
```
What is the use of the LEFT JOIN in SQL?
The LEFT JOIN in SQL is used to combine all rows from the left table and the matching rows from the right table, and returns NULL values for non-matching rows in the right table. The following query can be used to combine all rows from the left table and the matching rows from the right table:
```
SELECT column1, column2, ... 
FROM table1 
LEFT JOIN table2 ON table1.column = table2.column;
```
What is the use of the RIGHT JOIN in SQL?
The RIGHT JOIN in SQL is used to combine all rows from the right table and the matching rows from the left table, and returns NULL values for non-matching rows in the left table. The following query can be used to combine all rows from the right table and the matching rows from the left table:
```
SELECT column1, column2, ... 
FROM table1 
RIGHT JOIN table2 ON table1.column = table2.column;
```
What is the use of the FULL OUTER JOIN in SQL?
The FULL OUTER JOIN in SQL is used to combine all rows from both tables, and returns NULL values for non-matching rows in either the left or right table. The following query can be used to combine all rows from both tables:
```
SELECT column1, column2, ... 
FROM table1 
FULL OUTER JOIN table2 ON table1.column = table2.column;
```
What is the use of the IS NULL operator in SQL?
The IS NULL operator in SQL is used to test for NULL values. The following query can be used to select records with NULL values in a column:
```
SELECT column_name 
FROM table_name 
WHERE column_name IS NULL;
```
What is the use of the IS NOT NULL operator in SQL?
The IS NOT NULL operator in SQL is used to test for non-NULL values. The following query can be used to select records with non-NULL values in a column:
```
SELECT column_name 
FROM table_name 
WHERE column_name IS NOT NULL;
```
What is the use of the IN operator in SQL?
The IN operator in SQL is used to match values against a set of values. The following query can be used to select records with matching values in a column:
```
SELECT column_name 
FROM table_name 
WHERE column_name IN (value1, value2, ...);
```
What is the use of the NOT IN operator in SQL?
The NOT IN operator in SQL is used to exclude values that match a set of values. The following query can be used to select records that do not match the specified values in a column:
```
SELECT column_name 
FROM table_name 
WHERE column_name NOT IN (value1, value2, ...);
```
What is the use of the LIKE operator in SQL?
The LIKE operator in SQL is used to search for a specific pattern in a column. The following query can be used to select records that contain the specified pattern in a column:
```
SELECT column_name 
FROM table_name 
WHERE column_name LIKE 'pattern';
```
What is the use of the NOT LIKE operator in SQL?
The NOT LIKE operator in SQL is used to exclude records that contain a specific pattern in a column. The following query can be used to select records that do not contain the specified pattern in a column:
```
SELECT column_name 
FROM table_name 
WHERE column_name NOT LIKE 'pattern';
```
What is the use of the COUNT function in SQL?
The COUNT function in SQL is used to count the number of rows in a column. The following query can be used to count the number of rows in a column:
```
SELECT COUNT(column_name) 
FROM table_name;
```
What is the use of the SUM function in SQL?
The SUM function in SQL is used to calculate the sum of values in a column. The following query can be used to calculate the sum of values in a column: SELECT SUM(column_name) FROM table_name;
What is the use of the AVG function in SQL?
The AVG function in SQL is used to calculate the average of values in a column. The following query can be used to calculate the average of values in a column:
```
SELECT AVG(column_name) 
FROM table_name;
```
What is the use of the MIN function in SQL?
The MIN function in SQL is used to find the minimum value in a column. The following query can be used to find the minimum value in a column:
```
SELECT MIN(column_name) 
FROM table_name;
```
What is the use of the MAX function in SQL?
The MAX function in SQL is used to find the maximum value in a column. The following query can be used to find the maximum value in a column:
```
SELECT MAX(column_name) 
FROM table_name;
```
What is the use of the GROUP BY clause in SQL?
The GROUP BY clause in SQL is used to group rows that have the same values into summary rows, like finding the total number of items sold by each salesperson. The following query can be used to group rows by one or more columns:
```
SELECT column1, SUM(column2) 
FROM table_name GROUP BY column1;
```
What is the use of the DISTINCT keyword in SQL?
The DISTINCT keyword in SQL is used to return only unique values from a column in a table. The following query can be used to return unique values from a column:
```
SELECT DISTINCT column_name 
FROM table_name;
```
What is the use of the INNER JOIN clause in SQL?
The INNER JOIN clause in SQL is used to combine rows from two or more tables based on a related column between them. The following query can be used to combine rows from two tables based on a related column:
```
SELECT column1, column2 
FROM table1 
INNER JOIN table2 ON table1.column = table2.column;
```
What is the use of the LEFT JOIN clause in SQL?
The LEFT JOIN clause in SQL is used to combine all rows from the left table and matching rows from the right table. If there's no match, NULL values will be displayed for right table's columns. The following query can be used to combine all rows from the left table and matching rows from the right table:
```
SELECT column1, column2 
FROM table1 
LEFT JOIN table2 ON table1.column = table2.column;
```
What is the use of the RIGHT JOIN clause in SQL?
The RIGHT JOIN clause in SQL is used to combine all rows from the right table and matching rows from the left table. If there's no match, NULL values will be displayed for left table's columns. The following query can be used to combine all rows from the right table and matching rows from the left table:
```
SELECT column1, column2 
FROM table1 
RIGHT JOIN table2 ON table1.column = table2.column;
```
What is the use of the FULL OUTER JOIN clause in SQL?
The FULL OUTER JOIN clause in SQL is used to combine all rows from both tables. If there's no match, NULL values will be displayed for the columns of the table without a match. The following query can be used to combine all rows from both tables:
```
SELECT column1, column2 
FROM table1 
FULL OUTER JOIN table2 ON table1.column = table2.column;
```
How can you retrieve the first N records from a table in SQL?
You can retrieve the first N records from a table in SQL using the LIMIT keyword in the SELECT statement. For example, the following query will retrieve the first 5 records from the 'employees' table:
```
SELECT * 
FROM employees LIMIT 5;
```
How can you group data in SQL?
You can group data in SQL using the GROUP BY clause. The GROUP BY clause groups data based on one or more columns in a table. For example, the following query will group data in the 'employees' table by 'department' column:
```
SELECT department, SUM(salary) 
FROM employees GROUP BY department;
```
How can you sort data in SQL?
You can sort data in SQL using the ORDER BY clause. The ORDER BY clause sorts data in ascending or descending order based on one or more columns in a table. For example, the following query will sort data in the 'employees' table in ascending order based on the 'name' column:
```
SELECT * 
FROM employees ORDER BY name ASC;
```
What is the use of the HAVING clause in SQL?
The HAVING clause in SQL is used to filter data after it has been grouped by the GROUP BY clause. The HAVING clause operates on the results of the grouping rather than on individual rows. For example, the following query will group data in the 'employees' table by 'department' column and returns only those departments with a total salary greater than 10,000:
```
SELECT department, SUM(salary) 
FROM employees GROUP BY department HAVING SUM(salary) > 10000;
```
What is the use of the COUNT function in SQL?
The COUNT function in SQL is used to return the number of rows in a table or the number of rows that meet a specified condition. For example, the following query will return the number of rows in the 'employees' table:
```
SELECT COUNT(*) 
FROM employees;
```
What is the use of the AVG function in SQL?
The AVG function in SQL is used to return the average value of a numeric column in a table. For example, the following query will return the average salary of employees in the 'employees' table:
```
SELECT AVG(salary) 
FROM employees;
```
What is the use of the MAX function in SQL?
The MAX function in SQL is used to return the maximum value of a numeric column in a table. For example, the following query will return the maximum salary of employees in the 'employees' table:
```
SELECT MAX(salary) 
FROM employees;
```
What is the use of the MIN function in SQL?
The MIN function in SQL is used to return the minimum value of a numeric column in a table. For example, the following query will return the minimum salary of employees in the 'employees' table:
```
SELECT MIN(salary) 
FROM employees;
```
What is the use of the SUM function in SQL?
The SUM function in SQL is used to return the sum of values of a numeric column in a table. For example, the following query will return the total salary of employees in the 'employees' table:
```
SELECT SUM(salary) 
FROM employees;
```
What is a subquery in SQL?
A subquery in SQL is a query nested inside another query. The result of the subquery is used in the main query. For example, the following query will retrieve the name of the employee with the maximum salary in the 'employees' table: SELECT name FROM employees WHERE salary = (SELECT MAX(salary) FROM employees);
What is the use of the LIKE operator in SQL?
The LIKE operator in SQL is used to search for a specified pattern in a column. It uses wildcard characters such as '%' and '_' to match any number of characters or a single character respectively. For example, the following query will retrieve all employees whose name starts with 'J':
```
SELECT * 
FROM employees 
WHERE name LIKE 'J%';
```
What is the use of the IN operator in SQL?
The IN operator in SQL is used to determine if a value is present in a list of specified values. For example, the following query will retrieve all employees who work in departments with department id 1, 2, or 3:
```
SELECT * 
FROM employees 
WHERE department_id IN (1, 2, 3);
```
What is the use of the NOT IN operator in SQL?
The NOT IN operator in SQL is used to determine if a value is not present in a list of specified values. For example, the following query will retrieve all employees who do not work in departments with department id 1, 2, or 3:
```
SELECT * 
FROM employees 
WHERE department_id NOT IN (1, 2, 3);
```
What is the use of the BETWEEN operator in SQL?
The BETWEEN operator in SQL is used to determine if a value is within a specified range. For example, the following query will retrieve all employees with a salary between 50000 and 80000:
```
SELECT * 
FROM employees 
WHERE salary BETWEEN 50000 AND 80000;
```
What is the use of the NOT BETWEEN operator in SQL?
The NOT BETWEEN operator in SQL is used to determine if a value is not within a specified range. For example, the following query will retrieve all employees with a salary not between 50000 and 80000:
```
SELECT * 
FROM employees 
WHERE salary NOT BETWEEN 50000 AND 80000;
```
What is the use of the AVG function in SQL?
The AVG function in SQL is used to calculate the average value of a set of numbers. For example, the following query will retrieve the average salary of all employees:
```
SELECT AVG(salary) 
FROM employees;
```
What is the use of the SUM function in SQL?
The SUM function in SQL is used to calculate the sum of a set of numbers. For example, the following query will retrieve the total salary of all employees:
```
SELECT SUM(salary) 
FROM employees;
```
What is the use of the MIN function in SQL?
The MIN function in SQL is used to find the minimum value in a set of values. For example, the following query will retrieve the minimum salary of all employees:
```
SELECT MIN(salary) 
FROM employees;
```
What is the use of the MAX function in SQL?
The MAX function in SQL is used to find the maximum value in a set of values. For example, the following query will retrieve the maximum salary of all employees:
```
SELECT MAX(salary) 
FROM employees;
```
What is the use of the COUNT function in SQL?
The COUNT function in SQL is used to count the number of rows in a table. For example, the following query will retrieve the number of employees in the employees table:
```
SELECT COUNT(*) 
FROM employees;
```
What is the use of the GROUP BY clause in SQL?
The GROUP BY clause in SQL is used to group rows with identical values into summary rows. For example, the following query will group employees by department and retrieve the total salary of each department:
```
SELECT department, SUM(salary) 
FROM employees GROUP BY department;
```
What is the use of the DISTINCT keyword in SQL?
The DISTINCT keyword in SQL is used to remove duplicates from the results of a query. For example, the following query will retrieve a list of all unique departments:
```
SELECT DISTINCT department 
FROM employees;
```
What is the use of the UNION operator in SQL?
The UNION operator in SQL is used to combine the results of two or more SELECT statements into a single result set, removing duplicates in the process. For example, the following query will retrieve a list of all unique departments from two tables, employees and departments:
```
SELECT department 
FROM employees UNION SELECT department_name 
FROM departments;
```
What is the use of the INTERSECT operator in SQL?
The INTERSECT operator in SQL is used to combine the results of two SELECT statements and retrieve only the rows that appear in both results. For example, the following query will retrieve a list of departments that are common to both the employees and departments tables:
```
SELECT department 
FROM employees INTERSECT SELECT department_name 
FROM departments;
```
What is the use of the EXCEPT operator in SQL?
The EXCEPT operator in SQL is used to combine the results of two SELECT statements and retrieve only the rows that appear in the first result but not in the second. For example, the following query will retrieve a list of departments that are in the employees table but not in the departments table:
```
SELECT department 
FROM employees EXCEPT SELECT department_name 
FROM departments;
```
What is the use of the INNER JOIN clause in SQL?
The INNER JOIN clause in SQL is used to combine rows from two or more tables based on a related column between them. For example, the following query will retrieve a list of all employees and their departments:
```
SELECT employees.name, departments.department_name 
FROM employees 
INNER JOIN departments ON employees.department_id = departments.id;
```
What is the use of the LEFT JOIN clause in SQL?
The LEFT JOIN clause in SQL is used to combine rows from two or more tables based on a related column between them, including all rows from the left table and matching rows from the right table. If there is no match, the result will contain NULL values for the right table columns. For example, the following query will retrieve a list of all employees and their departments, including employees who do not have a department:
```
SELECT employees.name, departments.department_name 
FROM employees 
LEFT JOIN departments ON employees.department_id = departments.id;
```
What is the use of the RIGHT JOIN clause in SQL?
The RIGHT JOIN clause in SQL is used to combine rows from two or more tables based on a related column between them, including all rows from the right table and matching rows from the left table. If there is no match, the result will contain NULL values for the left table columns. For example, the following query will retrieve a list of all departments and their employees, including departments that do not have any employees:
```
SELECT employees.name, departments.department_name 
FROM employees 
RIGHT JOIN departments ON employees.department_id = departments.id;
```
What is the use of the FULL OUTER JOIN clause in SQL?
The FULL OUTER JOIN clause in SQL is used to combine rows from two or more tables based on a related column between them, including all rows from both tables and matching rows. If there is no match, the result will contain NULL values for the missing columns. For example, the following query will retrieve a list of all employees and their departments, including employees who do not have a department and departments that do not have any employees:
```
SELECT employees.name, departments.department_name 
FROM employees 
FULL OUTER JOIN departments ON employees.department_id = departments.id;
```
How to retrieve the top N rows in SQL?
To retrieve the top N rows in SQL, you can use the LIMIT clause. For example, the following query will retrieve the top 10 employees ordered by their salary in descending order:
```
SELECT * 
FROM employees ORDER BY salary DESC LIMIT 10;
```
How to update multiple rows in SQL?
To update multiple rows in SQL, you can use the UPDATE statement in conjunction with a WHERE clause that specifies the conditions for which rows should be updated. For example, the following query will increase the salary of all employees by 10%:
```
UPDATE employees SET salary = salary * 1.10 
WHERE department_id = 1;
```
How to delete multiple rows in SQL?
To delete multiple rows in SQL, you can use the DELETE statement in conjunction with a WHERE clause that specifies the conditions for which rows should be deleted. For example, the following query will delete all employees with a salary less than $50,000:
```
DELETE 
FROM employees 
WHERE salary < 50000;
```
How to create a new table in SQL?
To create a new table in SQL, you can use the CREATE TABLE statement along with the desired column names and data types. For example, the following query will create a new table named departments with three columns: id, department_name, and location:
```
CREATE TABLE departments (id INT PRIMARY KEY, department_name VARCHAR(50), location VARCHAR(50));
```
How to alter an existing table in SQL?
To alter an existing table in SQL, you can use the ALTER TABLE statement. For example, the following query will add a new column named budget to the departments table:
```
ALTER TABLE departments ADD COLUMN budget INT;
```
How to drop a table in SQL?
To drop a table in SQL, you can use the DROP TABLE statement. For example, the following query will drop the departments table:
```
DROP TABLE departments;
```
How to insert data into a table in SQL?
To insert data into a table in SQL, you can use the INSERT INTO statement along with the values for each column. For example, the following query will insert a new department into the departments table:
```
INSERT INTO departments (id, department_name, location) VALUES (1, 'Sales', 'New York');
```
How to join two tables in SQL?
To join two tables in SQL, you can use the JOIN clause. For example, the following query will retrieve the names of all employees and the name of their department by joining the employees and departments tables on the department_id column:
```
SELECT employees.name, departments.department_name 
FROM employees JOIN departments ON employees.department_id = departments.id;
```
How to group data in SQL?
To group data in SQL, you can use the GROUP BY clause along with aggregate functions such as SUM, AVG, MIN, MAX, or COUNT. For example, the following query will group employees by department and retrieve the average salary for each department:
```
SELECT department_id, AVG(salary) 
FROM employees GROUP BY department_id;
```
How to use a subquery in SQL?
To use a subquery in SQL, you can nest a SELECT statement within another SELECT statement. For example, the following query will retrieve the names of all employees who earn more than the average salary for their department:
```
SELECT name 
FROM employees 
WHERE salary > (SELECT AVG(salary) 
FROM employees 
WHERE department_id = employees.department_id);
```
How to use a case statement in SQL?
To use a case statement in SQL, you can use the CASE statement along with the WHEN, THEN, and END clauses. For example, the following query will retrieve the names of all employees along with a salary grade based on their salary:
```
SELECT name, CASE WHEN salary <= 50000 THEN 'A' WHEN salary <= 100000 THEN 'B' ELSE 'C' END AS salary_grade 
FROM employees;
```
How to use a self join in SQL?
To use a self join in SQL, you join a table to itself by using an alias for the same table. For example, the following query will retrieve the names of all employees who have the same manager:
```
SELECT e1.name, e2.name 
FROM employees e1 JOIN employees e2 ON e1.manager_id = e2.id 
WHERE e1.id != e2.id;
```
How to use a left join in SQL?
To use a left join in SQL, you can use the LEFT JOIN clause to include all the rows from the left table and matching rows from the right table. If there is no match, the right side's columns will be filled with NULL values. For example, the following query will retrieve the names of all departments along with the number of employees in each department:
```
SELECT departments.department_name, COUNT(employees.id) 
FROM departments 
LEFT JOIN employees ON departments.id = employees.department_id GROUP BY departments.department_name;
```
How to use a right join in SQL?
To use a right join in SQL, you can use the RIGHT JOIN clause to include all the rows from the right table and matching rows from the left table. If there is no match, the left side's columns will be filled with NULL values. For example, the following query will retrieve the names of all employees along with the names of the departments they work in:
```
SELECT employees.name, departments.department_name 
FROM employees 
RIGHT JOIN departments ON employees.department_id = departments.id;
```
How to use a full outer join in SQL?
To use a full outer join in SQL, you can use the FULL OUTER JOIN clause to include all the rows from both tables. If there is no match, the non-matching side's columns will be filled with NULL values. For example, the following query will retrieve the names of all employees along with the names of the departments they work in, including departments that have no employees:
```
SELECT employees.name, departments.department_name 
FROM employees 
FULL OUTER JOIN departments ON employees.department_id = departments.id;
```
How to use a cross join in SQL?
To use a cross join in SQL, you can use the CROSS JOIN clause to return all possible combinations of rows from the two tables. For example, the following query will retrieve the names of all employees along with the names of all departments:
```
SELECT employees.name, departments.department_name 
FROM employees CROSS JOIN departments;
```
How to use the DISTINCT keyword in SQL?
To use the DISTINCT keyword in SQL, you can include it in the SELECT clause to remove duplicates from the result set. For example, the following query will retrieve the names of all departments, with no duplicates:
```
SELECT DISTINCT department_name 
FROM departments;
```
How to use the GROUP BY clause in SQL?
To use the GROUP BY clause in SQL, you can include it in the query to group rows that have the same values in specified columns. You can then use aggregate functions such as COUNT, SUM, AVG, MIN, MAX, etc. on the grouped data. For example, the following query will retrieve the names of all departments along with the number of employees in each department:
```
SELECT department_name, COUNT(id) 
FROM employees GROUP BY department_name;
```
How to use the HAVING clause in SQL?
To use the HAVING clause in SQL, you can include it in the query after the GROUP BY clause to filter groups based on a specified condition. For example, the following query will retrieve the names of all departments with more than 5 employees:
```
SELECT department_name, COUNT(id) 
FROM employees GROUP BY department_name HAVING COUNT(id) > 5;
```
How to use the UNION operator in SQL?
To use the UNION operator in SQL, you can combine the result sets of two or more SELECT statements into a single result set, with duplicates removed. The number of columns and the data types of the columns must be the same in all SELECT statements. For example, the following query will retrieve the names of all employees from the employees table and all department names from the departments table:
```
SELECT name 
FROM employees UNION SELECT department_name 
FROM departments;
```
How to use the INTERSECT operator in SQL?
To use the INTERSECT operator in SQL, you can combine the result sets of two or more SELECT statements into a single result set, with only the rows that appear in all SELECT statements included. The number of columns and the data types of the columns must be the same in all SELECT statements. For example, the following query will retrieve the names of employees who work in both the 'Sales' and 'Marketing' departments:
```
SELECT name 
FROM employees 
WHERE department_name = 'Sales' INTERSECT SELECT name 
FROM employees 
WHERE department_name = 'Marketing';
```
How to use the MINUS operator in SQL?
To use the MINUS operator in SQL, you can subtract the result set of one SELECT statement from the result set of another SELECT statement. The number of columns and the data types of the columns must be the same in both SELECT statements. For example, the following query will retrieve the names of employees who work in the 'Sales' department but not in the 'Marketing' department:
```
SELECT name 
FROM employees 
WHERE department_name = 'Sales' MINUS SELECT name 
FROM employees 
WHERE department_name = 'Marketing';
```
How to use the JOIN clause in SQL?
To use the JOIN clause in SQL, you can combine the rows from two or more tables based on a related column between them. There are several types of JOINs such as INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL OUTER JOIN, etc. For example, the following query will retrieve the names of employees along with the names of their departments:
```
SELECT employees.name, departments.department_name 
FROM employees 
INNER JOIN departments ON employees.department_id = departments.id;
```
How to use the INNER JOIN clause in SQL?
To use the INNER JOIN clause in SQL, you can combine only the rows from two or more tables that have matching values in the related columns. For example, the following query will retrieve the names of employees along with the names of their departments:
```
SELECT employees.name, departments.department_name 
FROM employees 
INNER JOIN departments ON employees.department_id = departments.id;
```
How to use the LEFT JOIN clause in SQL?
To use the LEFT JOIN clause in SQL, you can combine all the rows from the left table (the first table in the query) and the matching rows from the right table (the second table in the query). If there is no matching row in the right table, NULL values will be displayed for the columns from the right table. For example, the following query will retrieve the names of all departments and the names of employees in each department:
```
SELECT departments.department_name, employees.name 
FROM departments 
LEFT JOIN employees ON departments.id = employees.department_id;
```
How to use the RIGHT JOIN clause in SQL?
To use the RIGHT JOIN clause in SQL, you can combine all the rows from the right table (the second table in the query) and the matching rows from the left table (the first table in the query). If there is no matching row in the left table, NULL values will be displayed for the columns from the left table. For example, the following query will retrieve the names of all employees and the names of departments in each employee works:
```
SELECT employees.name, departments.department_name 
FROM employees 
RIGHT JOIN departments ON employees.department_id = departments.id;
```

Top SQL Interview Questions for Entry-Level Candidates

What is SQL?

What are the different types of SQL commands?

What is the difference between a primary key and a foreign key?

What is a join in SQL?

What is a subquery in SQL?

What is a transaction in SQL?

What is an index in SQL?

What is a view in SQL?

What is a stored procedure in SQL?

What is a trigger in SQL?

What is the difference between a subquery and a join?

What is a correlated subquery in SQL?

What is a primary key in SQL?

What is a foreign key in SQL?

What is a unique constraint in SQL?

What is an index in SQL?

What is a clustered index in SQL?

What is a non-clustered index in SQL?

What is a view in SQL?

What is a stored procedure in SQL?

What is a transaction in SQL?

What is a trigger in SQL?

What is a cursor in SQL?

What is a temporary table in SQL?

What is a dynamic SQL in SQL?

What is a normalization in SQL?

What is a join in SQL?

What is a subquery in SQL?

What is a self-join in SQL?

What is a UNION in SQL?

What is a view in SQL?

What is a stored procedure in SQL?

What is a constraint in SQL?

What is a data type in SQL?

What is a primary key in SQL?

What is an index in SQL?

What is a transaction in SQL?

What is a trigger in SQL?

What is a foreign key in SQL?

What is a Cursor in SQL?

What is a subquery in SQL?

What is a join in SQL?

What is a union in SQL?

What is a self join in SQL?

What is a outer join in SQL?

What is a stored procedure in SQL?

What is a view in SQL?

What is a primary key in SQL?

What is a unique constraint in SQL?

What is a default constraint in SQL?

What is a transaction in SQL?

What is a trigger in SQL?

What is a constraint in SQL?

What is an index in SQL?

What is a normalization in SQL?

What is a join in SQL?

What is a subquery in SQL?

What is a self join in SQL?

What is a UNION in SQL?

What is a CASE statement in SQL?

What is a stored procedure in SQL?

What is a view in SQL?

What is a Cursor in SQL?

What is a primary key in SQL?

What is a foreign key in SQL?

What is an index in SQL?

What is a transaction in SQL?

What is a trigger in SQL?

What is a normalization in SQL?

What is a constraint in SQL?

What is indexing in SQL?

Top SQL Interview Questions for Experienced Candidates

What is SQL and what does it stand for?

Explain the difference between a primary key and a foreign key.

What is normalization in database management, and why is it important?

How do you create a table in SQL?

What is a join in SQL, and what are the different types of joins?

Explain the difference between a clustered and a non-clustered index.

How do you retrieve data from a table in SQL?