WHERE with OR operator in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the OR operator do in a SQL WHERE clause?

The OR operator allows you to filter rows that meet at least one of multiple conditions. If any condition separated by OR is true, the row is included in the result.

beginner

Write a simple SQL query using WHERE with OR to find employees in department 10 or department 20.

SELECT * FROM employees WHERE department_id = 10 OR department_id = 20;

beginner

Can you combine multiple OR conditions in a WHERE clause?

Yes, you can combine many OR conditions. For example: WHERE condition1 OR condition2 OR condition3. The row is included if any condition is true.

intermediate

How does SQL evaluate WHERE conditions with OR and AND together?

SQL evaluates AND before OR unless parentheses change the order. Use parentheses to group conditions clearly, e.g., WHERE (A OR B) AND C.

beginner

What happens if you use OR with conditions that never match any row?

If none of the OR conditions are true for a row, that row is excluded from the result. OR only includes rows where at least one condition is true.

Which SQL query finds rows where column A is 5 or column B is 10?

A SELECT * FROM table WHERE B = 10;

B SELECT * FROM table WHERE A = 5 AND B = 10;

C SELECT * FROM table WHERE A = 5;

D SELECT * FROM table WHERE A = 5 OR B = 10;

The OR operator includes rows where either A = 5 or B = 10 is true.

What does this query return? SELECT * FROM users WHERE age = 20 OR age = 30;

A Users who are exactly 20 or exactly 30 years old.

B Users who are between 20 and 30 years old.

C Users who are not 20 or 30 years old.

D Users who are both 20 and 30 years old.

OR checks if age is 20 or age is 30, so it returns users with either age.

How does SQL treat this condition? WHERE A = 1 OR B = 2 AND C = 3

A It treats AND before OR, so it's A=1 OR (B=2 AND C=3).

B It treats OR before AND, so it's (A=1 OR B=2) AND C=3.

C It treats all conditions equally and randomly.

D It causes a syntax error.

AND has higher precedence than OR, so it evaluates B=2 AND C=3 first.

Which is true about the OR operator in SQL WHERE clause?

A It returns rows where all conditions are true.

B It returns rows where at least one condition is true.

C It returns rows where no conditions are true.

D It returns rows only if conditions are false.

OR includes rows if any condition separated by OR is true.

What is the result of this query? SELECT * FROM products WHERE price < 10 OR price > 100;

A Products priced exactly 10 or 100.

B Products priced between 10 and 100.

C Products priced less than 10 or greater than 100.

D No products will be returned.

OR includes products with price less than 10 or greater than 100.

Explain how the OR operator works in a SQL WHERE clause and give a simple example.

Think about choosing between two or more options.

Describe how SQL evaluates WHERE conditions when both AND and OR operators are used together.

Remember the order of operations like in math.

Practice

1. What does the SQL WHERE clause with the OR operator do?

easy

A. It deletes rows that meet any condition.

B. It selects rows that meet at least one of the conditions.

C. It selects rows that meet all conditions simultaneously.

D. It updates rows that meet none of the conditions.

Solution

1. Step 1: Understand the WHERE clause

   The WHERE clause filters rows based on conditions.

2. Step 2: Understand the OR operator

   OR means if any condition is true, the row is selected.

3. Final Answer:

   It selects rows that meet at least one of the conditions. -> Option B

4. Quick Check:

   WHERE with OR = any condition true [OK]

Hint: OR means any condition true selects the row [OK]

Common Mistakes:

• Thinking OR requires all conditions true
• Confusing OR with AND
• Assuming OR deletes or updates rows

2. Which of the following SQL queries correctly uses the WHERE clause with the OR operator to find employees in department 10 or 20?

easy

A. SELECT * FROM employees WHERE department_id = 10 AND 20;

B. SELECT * FROM employees WHERE department_id = (10 OR 20);

C. SELECT * FROM employees WHERE department_id = 10 OR department_id = 20;

D. SELECT * FROM employees WHERE department_id IN 10 OR 20;

Solution

1. Step 1: Check correct OR syntax

   OR must connect full conditions: column = value OR column = value.

2. Step 2: Analyze each option

   A uses AND incorrectly; C uses invalid syntax; D misuses IN without parentheses.

3. Final Answer:

   SELECT * FROM employees WHERE department_id = 10 OR department_id = 20; -> Option C

4. Quick Check:

   Correct OR syntax = SELECT * FROM employees WHERE department_id = 10 OR department_id = 20; [OK]

Hint: Use OR between full conditions, not partial expressions [OK]

Common Mistakes:

• Using AND instead of OR
• Writing OR inside parentheses incorrectly
• Misusing IN without parentheses

3. Given the table products with columns id, name, and category, what rows will this query return?

SELECT * FROM products WHERE category = 'Books' OR category = 'Toys';

medium

A. Products in either 'Books' or 'Toys' categories.

B. Only products in both 'Books' and 'Toys' categories.

C. All products except those in 'Books' or 'Toys'.

D. No products because OR is invalid here.

Solution

1. Step 1: Understand the OR condition

   The query selects rows where category is 'Books' or 'Toys'.

2. Step 2: Determine matching rows

   Rows with category 'Books' or 'Toys' will be included, others excluded.

3. Final Answer:

   Products in either 'Books' or 'Toys' categories. -> Option A

4. Quick Check:

   OR selects rows matching any condition [OK]

Hint: OR includes rows matching any listed condition [OK]

Common Mistakes:

• Thinking OR means both conditions must be true
• Assuming OR excludes matching rows
• Believing OR causes syntax error

4. Identify the error in this SQL query:

SELECT * FROM orders WHERE status = 'Pending' OR;

medium

A. Missing condition after OR operator.

B. Incorrect use of WHERE clause.

C. OR operator should be AND.

D. No error, query is valid.

Solution

1. Step 1: Analyze the WHERE clause

   The WHERE clause ends with OR but no condition follows it.

2. Step 2: Understand OR syntax

   OR must connect two conditions; missing second condition causes syntax error.

3. Final Answer:

   Missing condition after OR operator. -> Option A

4. Quick Check:

   OR needs two conditions [OK]

Hint: OR must connect two conditions; don't leave it hanging [OK]

Common Mistakes:

• Leaving OR at end without condition
• Confusing OR with AND syntax
• Ignoring syntax errors in WHERE clause

5. You have a table students with columns id, grade, and city. Write a query to select students who have grade 'A' or live in 'New York' or 'Los Angeles'. Which query is correct?

hard

A. SELECT * FROM students WHERE grade = 'A' OR city = 'New York' OR 'Los Angeles';

B. SELECT * FROM students WHERE grade = 'A' AND city = 'New York' OR 'Los Angeles';

C. SELECT * FROM students WHERE grade = 'A' OR city = 'New York' AND city = 'Los Angeles';

D. SELECT * FROM students WHERE grade = 'A' OR city IN ('New York', 'Los Angeles');

Solution

1. Step 1: Understand the conditions

   Select students with grade 'A' OR city 'New York' OR city 'Los Angeles'.

2. Step 2: Analyze each query

   A has syntax error (missing column in last condition); B has syntax error and wrong logic; C has incorrect logic due to AND; D is correct and concise using IN.

3. Final Answer:

   SELECT * FROM students WHERE grade = 'A' OR city IN ('New York', 'Los Angeles'); -> Option D

4. Quick Check:

   Use OR with IN for multiple values [OK]

Hint: Use OR with IN for multiple city values [OK]

Common Mistakes:

• Using AND between city conditions
• Omitting column name after OR
• Syntax errors with OR and IN