IF function in MySQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the IF function do in MySQL?

The IF function checks a condition and returns one value if the condition is true, and another value if it is false.

beginner

Write the syntax of the IF function in MySQL.

IF(condition, value_if_true, value_if_false)

intermediate

How does the IF function differ from the CASE statement in MySQL?

IF is used for simple two-way decisions (true/false), while CASE can handle multiple conditions and outcomes.

beginner

Example: What will this query return? SELECT IF(5 > 3, 'Yes', 'No');

It will return 'Yes' because 5 is greater than 3, so the condition is true.

intermediate

Can the IF function be nested inside another IF function in MySQL?

Yes, you can nest IF functions to check multiple conditions step-by-step.

What will this MySQL query return? SELECT IF(10 = 10, 'Equal', 'Not Equal');

A NULL

B 'Not Equal'

C 'Equal'

D Error

The condition 10 = 10 is true, so IF returns 'Equal'.

Which part of IF(condition, value_if_true, value_if_false) is evaluated first?

A All at once

B value_if_true

C value_if_false

D condition

The condition is evaluated first to decide which value to return.

Can IF function return NULL as a value_if_true or value_if_false?

A Yes

B No

C Only value_if_true can be NULL

D Only value_if_false can be NULL

IF can return NULL for either true or false results.

Which of these is a valid use of IF in MySQL?

A SELECT IF age >= 18, 'Adult', 'Minor' FROM users;

B SELECT IF(age >= 18, 'Adult', 'Minor') FROM users;

C SELECT IF(age >= 18 THEN 'Adult' ELSE 'Minor') FROM users;

D SELECT IF(age >= 18 'Adult', 'Minor') FROM users;

Option B uses correct IF syntax with condition and two values.

What happens if the condition in IF is NULL?

A IF returns value_if_false

B IF returns value_if_true

C IF returns NULL

D IF throws an error

If condition is NULL, it is treated as false, so IF returns value_if_false.

Explain how the IF function works in MySQL and give a simple example.

Think about a question with two possible answers.

Describe a situation where nesting IF functions would be useful in a database query.

Imagine checking age groups or multiple categories.

Practice

1. What does the MySQL IF function do?

easy

A. Returns one value if a condition is true, another if false

B. Loops through rows in a table

C. Deletes rows based on a condition

D. Creates a new table

Solution

1. Step 1: Understand the purpose of IF function

   The IF function checks a condition and returns one value if true, another if false.

2. Step 2: Compare options with this behavior

   Only Returns one value if a condition is true, another if false describes this behavior correctly; others describe unrelated actions.

3. Final Answer:

   Returns one value if a condition is true, another if false -> Option A

4. Quick Check:

   IF function = conditional value choice [OK]

Hint: IF returns two possible values based on one condition [OK]

Common Mistakes:

• Thinking IF loops through rows
• Confusing IF with DELETE or CREATE
• Assuming IF creates tables

2. Which of the following is the correct syntax for the MySQL IF function?

easy

A. IF[condition] {true_value} ELSE {false_value}

B. IF condition THEN true_value ELSE false_value END

C. IF(condition, true_value, false_value)

D. IF condition ? true_value : false_value

Solution

1. Step 1: Recall MySQL IF function syntax

   MySQL IF function uses parentheses and commas: IF(condition, true_value, false_value).

2. Step 2: Check each option

   IF(condition, true_value, false_value) matches correct syntax; the THEN/ELSE/END version is PL/SQL style, the bracketed version and ternary operator are invalid in MySQL.

3. Final Answer:

   IF(condition, true_value, false_value) -> Option C

4. Quick Check:

   Correct syntax uses parentheses and commas [OK]

Hint: IF uses parentheses and commas, not keywords or symbols [OK]

Common Mistakes:

• Using IF without parentheses
• Confusing IF with procedural IF syntax
• Using brackets or ternary operators

3. Given a table employees with a column salary, what will this query return?

SELECT name, IF(salary >= 5000, 'High', 'Low') AS salary_level FROM employees;

medium

A. An error because IF cannot be used in SELECT

B. Only employees with salary ≥ 5000

C. Salary values replaced by 'High' or 'Low'

D. Names with 'High' if salary ≥ 5000, else 'Low'

Solution

1. Step 1: Understand the IF condition in SELECT

   The IF checks if salary is 5000 or more; returns 'High' if true, else 'Low'.

2. Step 2: Analyze the query output

   The query returns each employee's name and a label 'High' or 'Low' in salary_level column.

3. Final Answer:

   Names with 'High' if salary ≥ 5000, else 'Low' -> Option D

4. Quick Check:

   IF labels salary levels, does not filter rows [OK]

Hint: IF in SELECT returns values, does not filter rows [OK]

Common Mistakes:

• Thinking IF filters rows like WHERE
• Assuming salary values are replaced
• Believing IF causes syntax error in SELECT

4. Identify the error in this MySQL query using IF:

SELECT name, IF salary > 1000, 'Rich', 'Poor' AS status FROM users;

medium

A. Missing FROM keyword

B. Missing parentheses around IF arguments

C. IF cannot be used in SELECT clause

D. Wrong column name 'status'

Solution

1. Step 1: Check IF function syntax

   IF requires parentheses around condition and values: IF(condition, true_value, false_value).

2. Step 2: Identify error in query

   The query lacks parentheses around IF arguments, causing syntax error.

3. Final Answer:

   Missing parentheses around IF arguments -> Option B

4. Quick Check:

   IF needs parentheses for arguments [OK]

Hint: Always use parentheses with IF arguments [OK]

Common Mistakes:

• Omitting parentheses in IF
• Confusing alias placement
• Thinking IF is not allowed in SELECT

5. You want to classify products as 'Expensive', 'Moderate', or 'Cheap' based on price:
- Price > 1000: 'Expensive'
- Price between 500 and 1000: 'Moderate'
- Price < 500: 'Cheap'
Which query correctly uses nested IF functions to achieve this?

hard

A. SELECT product_name, IF(price > 1000, 'Expensive', IF(price >= 500, 'Moderate', 'Cheap')) AS price_category FROM products;

B. SELECT product_name, IF(price > 1000, 'Expensive', 'Moderate', 'Cheap') AS price_category FROM products;

C. SELECT product_name, IF(price > 1000, 'Expensive') ELSE IF(price >= 500, 'Moderate') ELSE 'Cheap' AS price_category FROM products;

D. SELECT product_name, IF(price > 1000, 'Expensive', IF(price > 500, 'Moderate', 'Cheap')) AS price_category FROM products;

Solution

1. Step 1: Understand nested IF logic

   First IF checks if price > 1000, else second IF checks if price ≥ 500, else 'Cheap'.

2. Step 2: Evaluate each option

   The version with ELSE IF uses invalid syntax. The version with four arguments has too many arguments for IF. The version with inner IF(price > 500, ...) misses 'Moderate' for price = 500. SELECT product_name, IF(price > 1000, 'Expensive', IF(price >= 500, 'Moderate', 'Cheap')) AS price_category FROM products; correctly nests IF with proper conditions and values.

3. Final Answer:

   SELECT product_name, IF(price > 1000, 'Expensive', IF(price >= 500, 'Moderate', 'Cheap')) AS price_category FROM products; -> Option A

4. Quick Check:

   Nested IF with correct conditions and syntax [OK]

Hint: Nest IF inside ELSE part with correct conditions [OK]

Common Mistakes:

• Using too many arguments in one IF
• Incorrect nested IF syntax
• Wrong comparison operators in conditions