UPDATE with WHERE clause in MySQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output after this UPDATE?

Consider a table Employees with columns id, name, and salary. Initially, the table has:

1, 'Alice', 5000
2, 'Bob', 6000
3, 'Charlie', 7000

What will be the salary of Bob after running this query?

UPDATE Employees SET salary = salary + 500 WHERE name = 'Bob';

A 6500

B 5500

C 7000

D 6000

💡 Hint

The WHERE clause limits which rows get updated.

Only Bob's salary is increased by 500, so 6000 + 500 = 6500.

📝 Syntax

intermediate

Which UPDATE query is syntactically correct?

Choose the correct MySQL UPDATE statement that increases salary by 1000 for employees with salary less than 6000.

A UPDATE Employees SET salary = salary + 1000 WHERE salary < 6000;

B UPDATE Employees salary = salary + 1000 WHERE salary < 6000;

C UPDATE Employees SET salary + 1000 WHERE salary < 6000;

D UPDATE Employees SET salary = salary + 1000 salary < 6000;

💡 Hint

Remember the syntax: UPDATE table SET column = value WHERE condition;

Option A follows correct syntax with SET and WHERE clauses properly used.

❓ optimization

advanced

Which UPDATE query is more efficient for updating multiple rows?

You want to increase salary by 500 for all employees in department 'Sales'. The table has an index on the department column.
Which query is more efficient?

A UPDATE Employees SET salary = salary + 500 WHERE department LIKE '%Sales%';

B UPDATE Employees SET salary = salary + 500 WHERE department = 'Sales';

C UPDATE Employees SET salary = salary + 500;

D UPDATE Employees SET salary = salary + 500 WHERE department != 'Sales';

💡 Hint

Using indexed columns in WHERE clause improves performance.

Option B uses the indexed column with an exact match, making it efficient.

🔧 Debug

advanced

What error does this UPDATE query raise?

Given a table Products with columns id, name, and price, what error occurs when running:

UPDATE Products SET price = price + 10 WHERE;

A Runtime error: column 'price' not found

B No error, updates all rows

C Syntax error near 'WHERE;'

D Type error: cannot add integer to price

💡 Hint

Check the WHERE clause syntax.

The WHERE clause is incomplete and causes a syntax error.

🧠 Conceptual

expert

What happens if UPDATE has no WHERE clause?

If you run:

UPDATE Employees SET salary = salary + 1000;

What is the effect on the table?

A Syntax error due to missing WHERE clause

B Only rows with NULL salary are updated

C No rows are updated

D All rows have their salary increased by 1000

💡 Hint

Think about what happens when WHERE is omitted.

Without WHERE, UPDATE affects every row in the table.