MySQL SQL Execution Order Quiz: Test Your Knowledge

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True / False

In MySQL, the SELECT clause is executed before the WHERE clause.

True False

In MySQL, the WHERE clause is executed before the SELECT clause. The execution order begins with the FROM clause, followed by WHERE, GROUP BY, HAVING, SELECT, ORDER BY, and finally LIMIT.

True / False

In MySQL, the FROM clause is always executed first.

True False

The FROM clause is the starting point of query execution in MySQL, as it determines the tables from which data will be retrieved.

True / False

The ORDER BY clause in MySQL is executed before the GROUP BY clause.

True False

The GROUP BY clause is executed before the ORDER BY clause. GROUP BY groups the rows and performs aggregate functions, while ORDER BY sorts the result set.

True / False

In MySQL, the HAVING clause can filter records before the GROUP BY clause.

True False

The HAVING clause is used to filter groups created by the GROUP BY clause, so it is executed after GROUP BY.

True / False

In MySQL, the LIMIT clause is always executed last.

True False

The LIMIT clause is executed last in the execution order to restrict the number of rows returned by the query.

True / False

In MySQL, the JOIN operations are performed before the WHERE clause is evaluated.

True False

JOIN operations (in the FROM clause) are performed before the WHERE clause filters the rows from the joined tables.

True / False

In MySQL, subqueries in the SELECT clause are executed before the WHERE clause.

True False

Subqueries in the SELECT clause are evaluated after the main query's WHERE clause has filtered the rows.

True / False

In MySQL, the DISTINCT keyword is applied before the ORDER BY clause.

True False

The DISTINCT keyword is applied before sorting the results with the ORDER BY clause, ensuring that duplicates are removed before sorting.

True / False

In MySQL, window functions are evaluated after the WHERE and GROUP BY clauses but before the ORDER BY clause.

True False

Window functions are evaluated after the rows are filtered by the WHERE clause and grouped by the GROUP BY clause, but before the final sorting by the ORDER BY clause.

Q10

True / False

In MySQL, the WITH clause (Common Table Expressions) is executed before the main query.

True False

Window functions are evaluated after the rows are filtered by the WHERE clause and grouped by the GROUP BY clause, but before the final sorting by the ORDER BY clause.

Q11

Single Choice

Which of the following statements is executed first in a MySQL query?

SELECT WHERE FROMORDER BY

In SQL, the execution order starts with the FROM clause, which determines the source tables for the query.

Q12

Single Choice

What will be the result of the following MySQL query?

SQL Code

SELECT COUNT(*)
FROM employees;

The total number of columns in the employees table The total number of rows in the employees table The total number of rows where the columns are not nullThe total number of unique rows in the employees table

COUNT(*) counts all rows in the employees table, regardless of NULL values.

Q13

Single Choice

In MySQL, what does the following SQL command do?

SQL Code

DELETE FROM products WHERE product_id = 10;

Deletes all products Deletes the row with product_id equal to 10 Deletes the product_id column from the tableDrops the products table Answer: B) Deletes the row with product_id equal to 10

The DELETE statement removes the row where product_id equals 10 from the products table.

Q14

Single Choice

Which statement is true about this query execution?

SQL Code

Consider the following query:
SELECT department, SUM(salary)
FROM employees
GROUP BY department
HAVING SUM(salary) > 100000;

The GROUP BY clause is executed after the HAVING clause The SUM(salary) is calculated before the GROUP BY clause The HAVING clause filters groups after the GROUP BY has been executedThe SELECT clause is executed before the FROM clause Answer: C) The HAVING clause filters groups after the GROUP BY has been executed

The HAVING clause filters the groups that result from the GROUP BY clause, based on the specified condition.

Q15

Single Choice

What will the following MySQL query return?

SQL Code

SELECT employee_name, salary * 1.10 AS adjusted_salary
FROM employees
WHERE salary > 50000;

Employee names with a 10% salary increase for those with salaries over 50,000 Employee names with a 10% salary decrease for those with salaries over 50,000 Employee names with their current salaryEmployee names with their salary increased by 50%

The query selects employees with a salary greater than 50,000 and calculates their adjusted salary by increasing it by 10%.

Q16

Single Choice

Which MySQL clause is responsible for limiting the number of records returned by a query?

LIMIT GROUP BY ORDER BYHAVING

The LIMIT clause restricts the number of rows returned by a query, making it useful for pagination or returning a subset of data.

Q17

Single Choice

What does the following MySQL query achieve?

SQL Code

SELECT employee_id,
 (SELECT department_name FROM departments WHERE departments.department_id = employees.department_id) AS department
FROM employees;

It performs a self-join on the employees table It retrieves employee IDs along with the department names from a related table It returns only employees who belong to a specific departmentIt calculates the total salary for each department

This query uses a subquery to retrieve the department name for each employee by matching department_id in both the employees and departments tables.

Q18

Single Choice

In MySQL, which of the following describes how subqueries are executed?

Subqueries are always executed after the main query Subqueries are executed in the order they appear in the query Subqueries are executed first, before the main querySubqueries are executed simultaneously with the main query

Subqueries are evaluated first to provide a result that is then used by the main query.

Q19

Single Choice

What is the purpose of the following MySQL query?

SQL Code

UPDATE employees
SET salary = salary * 1.05
WHERE employee_id IN (SELECT employee_id FROM bonuses WHERE bonus > 5000);

It increases the salary of all employees It increases the salary of employees who received a bonus greater than 5000 It increases the salary by 5% for all employeesIt resets the salary of employees who received a bonus greater than 5000

The query updates the salary of employees whose employee_id matches those who received a bonus greater than 5000.

Q20

Single Choice

What can be inferred from the execution plan output if the type column shows index?

SQL Code

Consider the following MySQL query execution plan:
EXPLAIN SELECT * FROM orders WHERE order_date > '2024-01-01' ORDER BY customer_id LIMIT 10;

The query is using a full table scan The query is using an index scan, which is faster than a full table scan The query is using a temporary tableThe query does not use any index

If the type column in the execution plan shows index, it means the query is scanning the index, which is generally faster than a full table scan.

Q21

Multiple Choice

Which SQL query correctly demonstrates the execution order from WHERE to GROUP BY?

SQL Code

SELECT department, COUNT(*)
FROM employees
WHERE salary > 50000
GROUP BY department;

SELECT department, COUNT(*) FROM employees WHERE salary > 50000 GROUP BY department; SELECT department, COUNT(*) GROUP BY department WHERE salary > 50000 FROM employees; SELECT department, COUNT(*) WHERE salary > 50000 FROM employees GROUP BY department;SELECT department, COUNT(*) GROUP BY department FROM employees WHERE salary > 50000;

The correct execution order is FROM -> WHERE -> GROUP BY -> SELECT. The WHERE clause filters rows before the GROUP BY clause aggregates them.

Q22

Multiple Choice

Identify the SQL query that correctly demonstrates the execution order including JOIN operations.

SQL Code

SELECT e.name, d.department_name
FROM employees e
JOIN departments d ON e.department_id = d.department_id
WHERE e.salary > 50000;

SELECT e.name, d.department_name FROM employees e JOIN departments d ON e.department_id = d.department_id WHERE e.salary > 50000; SELECT e.name, d.department_name WHERE e.salary > 50000 FROM employees e JOIN departments d ON e.department_id = d.department_id; SELECT e.name, d.department_name JOIN departments d ON e.department_id = d.department_id FROM employees e WHERE e.salary > 50000;SELECT e.name, d.department_name FROM employees e WHERE e.salary > 50000 JOIN departments d ON e.department_id = d.department_id;

The correct execution order is FROM -> JOIN -> ON -> WHERE -> SELECT. The JOIN operation is performed before the WHERE clause filters the results.

Q23

Multiple Choice

Which SQL query demonstrates the execution order involving a subquery in the WHERE clause?

SQL Code

SELECT name
FROM employees
WHERE department_id IN (SELECT department_id FROM departments WHERE department_name = 'Sales');

SELECT name FROM employees WHERE department_id IN (SELECT department_id FROM departments WHERE department_name = 'Sales'); SELECT name FROM employees WHERE department_id = (SELECT department_id FROM departments WHERE department_name = 'Sales'); SELECT name WHERE department_id IN (SELECT department_id FROM departments WHERE department_name = 'Sales') FROM employees;SELECT name FROM employees WHERE department_id IN (SELECT department_id FROM departments WHERE department_name = 'Sales') AND salary > 60000;

The correct execution order for the subquery is FROM -> WHERE -> SELECT (inside the subquery) before the outer query WHERE clause filters based on its results.

Q24

Multiple Choice

Determine the SQL query that correctly uses the execution order with HAVING after GROUP BY.

SQL Code

SELECT department, COUNT(*)
FROM employees
GROUP BY department
HAVING COUNT(*) > 5;

SELECT department, COUNT(*) FROM employees GROUP BY department HAVING COUNT(*) > 5; SELECT department, COUNT(*) HAVING COUNT(*) > 5 FROM employees GROUP BY department; SELECT department, COUNT(*) GROUP BY department FROM employees HAVING COUNT(*) > 5;SELECT department, COUNT(*) FROM employees HAVING COUNT(*) > 5 GROUP BY department;

The correct execution order is FROM -> WHERE -> GROUP BY -> HAVING -> SELECT. The HAVING clause filters groups after the aggregation is done.

Q25

Multiple Choice

Which SQL query correctly demonstrates the use of ORDER BY after SELECT?

SQL Code

SELECT name, salary
FROM employees
WHERE department_id = 3
ORDER BY salary DESC;

SELECT name, salary FROM employees WHERE department_id = 3 ORDER BY salary DESC; SELECT name, salary ORDER BY salary DESC WHERE department_id = 3 FROM employees; SELECT name, salary FROM employees ORDER BY salary DESC WHERE department_id = 3;SELECT name, salary WHERE department_id = 3 FROM employees ORDER BY salary DESC;

The correct execution order is FROM -> WHERE -> SELECT -> ORDER BY. The ORDER BY clause sorts the result set after the SELECT operation.

Q26

Multiple Choice

Which SQL query illustrates the correct execution order when combining DISTINCT and GROUP BY?

SQL Code

SELECT DISTINCT department_id
FROM employees
GROUP BY department_id;

SELECT DISTINCT department_id FROM employees GROUP BY department_id; SELECT department_id FROM employees GROUP BY department_id DISTINCT; SELECT DISTINCT department_id GROUP BY department_id FROM employees;SELECT department_id GROUP BY department_id FROM employees DISTINCT;

The correct execution order is FROM -> GROUP BY -> DISTINCT -> SELECT. DISTINCT is applied after the GROUP BY operation to ensure unique groups.

Q27

Multiple Choice

Identify the SQL query that correctly orders the operations for LIMIT after ORDER BY.

SQL Code

SELECT name, salary
FROM employees
ORDER BY salary DESC
LIMIT 10;

SELECT name, salary FROM employees ORDER BY salary DESC LIMIT 10; SELECT name, salary LIMIT 10 FROM employees ORDER BY salary DESC; SELECT name, salary ORDER BY salary DESC FROM employees LIMIT 10;SELECT name, salary FROM employees LIMIT 10 ORDER BY salary DESC;

The correct execution order is FROM -> SELECT -> ORDER BY -> LIMIT. The LIMIT clause restricts the number of rows returned after sorting by ORDER BY.

Q28

Multiple Choice

Which SQL query demonstrates the correct execution order for a query that uses both JOIN and WHERE?

SQL Code

SELECT e.name, d.department_name
FROM employees e
JOIN departments d ON e.department_id = d.department_id
WHERE d.department_name = 'Sales';

SELECT e.name, d.department_name FROM employees e JOIN departments d ON e.department_id = d.department_id WHERE d.department_name = 'Sales'; SELECT e.name, d.department_name WHERE d.department_name = 'Sales' FROM employees e JOIN departments d ON e.department_id = d.department_id; SELECT e.name, d.department_name JOIN departments d ON e.department_id = d.department_id FROM employees e WHERE d.department_name = 'Sales';SELECT e.name, d.department_name FROM employees e WHERE d.department_name = 'Sales' JOIN departments d ON e.department_id = d.department_id;

The correct execution order is FROM -> JOIN -> ON -> WHERE -> SELECT. The WHERE clause filters the result after the JOIN operation is completed.

Q29

Multiple Choice

Determine the SQL query that follows the correct execution order when using a subquery in the SELECT clause.

SQL Code

SELECT name, (SELECT department_name FROM departments WHERE department_id = e.department_id) AS dept_name
FROM employees e;

SELECT name, (SELECT department_name FROM departments WHERE department_id = e.department_id) AS dept_name FROM employees e; SELECT name, dept_name FROM employees e (SELECT department_name AS dept_name FROM departments WHERE department_id = e.department_id); SELECT name, (SELECT department_name FROM departments WHERE department_id = e.department_id) AS dept_name WHERE department_id = e.department_id FROM employees e;SELECT name FROM employees e WHERE department_id = e.department_id SELECT department_name FROM departments;

The correct execution order for the subquery in the SELECT clause is FROM -> WHERE -> SELECT inside the subquery, which is executed first before the outer query's SELECT.

Q30

Multiple Choice

Which SQL query demonstrates the correct execution order for complex queries with multiple clauses, including WHERE, GROUP BY, HAVING, and ORDER BY?

SQL Code

SELECT department, COUNT(*) AS num_employees
FROM employees
WHERE salary > 50000
GROUP BY department
HAVING num_employees > 10
ORDER BY num_employees DESC;

SELECT department, COUNT(*) AS num_employees FROM employees WHERE salary > 50000 GROUP BY department HAVING num_employees > 10 ORDER BY num_employees DESC; SELECT department, COUNT(*) AS num_employees GROUP BY department HAVING num_employees > 10 WHERE salary > 50000 ORDER BY num_employees DESC FROM employees; SELECT department, COUNT(*) AS num_employees FROM employees HAVING num_employees > 10 GROUP BY department WHERE salary > 50000 ORDER BY num_employees DESC;SELECT department, COUNT(*) AS num_employees WHERE salary > 50000 GROUP BY department FROM employees HAVING num_employees > 10 ORDER BY num_employees DESC;

The correct execution order is FROM -> WHERE -> GROUP BY -> HAVING -> SELECT -> ORDER BY. Each clause is executed in sequence to produce the final sorted result.

MySQL Database Quiz Questions