UPPER and LOWER in MySQL

Introduction

UPPER and LOWER help change text to all uppercase or all lowercase letters. This makes text easier to compare or display consistently.

When you want to make sure names are shown in all capital letters on a report.

When you need to compare two words without worrying about letter case differences.

When cleaning up user input to store all text in lowercase for consistency.

When searching for words in a database ignoring uppercase or lowercase differences.

Syntax

MySQL

UPPER(text)
LOWER(text)

Replace 'text' with the column name or string you want to change.

These functions return a new string with all letters changed to upper or lower case.

Examples

Changes the string 'hello world' to all uppercase letters.

MySQL

SELECT UPPER('hello world');

Changes the string 'HELLO WORLD' to all lowercase letters.

MySQL

SELECT LOWER('HELLO WORLD');

Shows all employee names in uppercase letters.

MySQL

SELECT UPPER(name) FROM employees;

Shows all customer city names in lowercase letters.

MySQL

SELECT LOWER(city) FROM customers;

Sample Program

This creates a table with usernames in mixed cases. Then it shows each username in uppercase and lowercase.

MySQL

CREATE TABLE users (id INT, username VARCHAR(20));
INSERT INTO users VALUES (1, 'Alice'), (2, 'Bob'), (3, 'CHARLIE');
SELECT id, UPPER(username) AS upper_name, LOWER(username) AS lower_name FROM users;

Important Notes

UPPER and LOWER only affect letters; numbers and symbols stay the same.

These functions are useful for case-insensitive searches when combined with WHERE clauses.

Remember that the output is a new string; the original data in the table does not change unless you update it.

Summary

UPPER(text) converts all letters in text to uppercase.

LOWER(text) converts all letters in text to lowercase.

Use these functions to standardize text for display or comparison.

Practice

1. What does the MySQL function UPPER('hello') return?

easy

A. 'heLLo'

B. 'hello'

C. 'Hello'

D. 'HELLO'

Solution

1. Step 1: Understand the UPPER function

   The UPPER function converts all letters in the input text to uppercase letters.

2. Step 2: Apply UPPER to 'hello'

   Applying UPPER to 'hello' changes all letters to uppercase, resulting in 'HELLO'.

3. Final Answer:

   'HELLO' -> Option D

4. Quick Check:

   UPPER('hello') = 'HELLO' [OK]

Hint: UPPER makes all letters capital [OK]

Common Mistakes:

• Thinking UPPER only capitalizes first letter
• Confusing UPPER with LOWER
• Expecting mixed case output

2. Which of the following is the correct syntax to convert the column name to lowercase in a SELECT query?

easy

A. SELECT LOWER(name) FROM users;

B. SELECT LOWER name FROM users;

C. SELECT name.LOWER() FROM users;

D. SELECT LOWER[name] FROM users;

Solution

1. Step 1: Recall correct function syntax

   MySQL functions use the format FUNCTION_NAME(argument), so LOWER(name) is correct.

2. Step 2: Check each option

   SELECT LOWER(name) FROM users; uses correct syntax: LOWER(name). Options A, B, and D use invalid syntax forms.

3. Final Answer:

   SELECT LOWER(name) FROM users; -> Option A

4. Quick Check:

   Correct function call syntax = SELECT LOWER(name) FROM users; [OK]

Hint: Use function_name(column) syntax for MySQL functions [OK]

Common Mistakes:

• Omitting parentheses around column
• Using dot or bracket notation incorrectly
• Writing function name in lowercase without parentheses

3. Given a table products with a column category containing values 'Books', 'electronics', 'TOYS', what will the query SELECT DISTINCT UPPER(category) FROM products; return?

medium

A. ['Books', 'electronics', 'TOYS']

B. ['BOOKS', 'ELECTRONICS', 'TOYS']

C. ['books', 'electronics', 'toys']

D. ['BOOKS', 'electronics', 'TOYS']

Solution

1. Step 1: Understand UPPER and DISTINCT

   UPPER converts all text to uppercase. DISTINCT removes duplicates from the result set.

2. Step 2: Apply UPPER to each category value

   'Books' -> 'BOOKS', 'electronics' -> 'ELECTRONICS', 'TOYS' -> 'TOYS'. All become uppercase.

3. Step 3: Collect distinct uppercase values

   All three are unique after conversion, so the result is ['BOOKS', 'ELECTRONICS', 'TOYS'].

4. Final Answer:

   ['BOOKS', 'ELECTRONICS', 'TOYS'] -> Option B

5. Quick Check:

   UPPER + DISTINCT = uppercase unique values [OK]

Hint: UPPER changes all letters; DISTINCT removes duplicates [OK]

Common Mistakes:

• Expecting original case values
• Ignoring DISTINCT effect
• Mixing uppercase and lowercase in output

4. Consider the query: SELECT LOWER('MySQL') FROM dual. It returns an error. What is the likely cause?

medium

A. The table 'dual' does not exist in MySQL by default

B. LOWER function is not supported in MySQL

C. The string 'MySQL' must be in uppercase already

D. Missing semicolon at the end of the query

Solution

1. Step 1: Understand the use of 'dual'

   'dual' is a special table in Oracle but not present by default in MySQL.

2. Step 2: Check MySQL behavior

   MySQL does not require 'FROM dual' for selecting expressions; using it causes an error if 'dual' table is missing.

3. Final Answer:

   The table 'dual' does not exist in MySQL by default -> Option A

4. Quick Check:

   MySQL lacks default 'dual' table [OK]

Hint: MySQL doesn't need 'FROM dual' for expressions [OK]

Common Mistakes:

• Assuming 'dual' exists like in Oracle
• Thinking LOWER is unsupported
• Blaming missing semicolon

5. You want to find all users in the users table whose email ends with '@example.com', ignoring case differences. Which query correctly uses UPPER or LOWER to achieve this?

hard

A. SELECT * FROM users WHERE LOWER(email) LIKE '[e-mail]';

B. SELECT * FROM users WHERE LOWER(email) LIKE '[e-mail]';

C. SELECT * FROM users WHERE UPPER(email) LIKE '[e-mail]';

D. SELECT * FROM users WHERE email LIKE '[e-mail]';

Solution

1. Step 1: Understand case-insensitive matching

   To ignore case, convert both sides to the same case before comparing.

2. Step 2: Apply UPPER to email and pattern

   Using UPPER(email) and matching with uppercase pattern '[e-mail]' ensures case-insensitive match.

3. Step 3: Check options

   SELECT * FROM users WHERE UPPER(email) LIKE '[e-mail]'; correctly uses UPPER on email and uppercase pattern. SELECT * FROM users WHERE LOWER(email) LIKE '[e-mail]'; mismatches case in pattern. SELECT * FROM users WHERE email LIKE '[e-mail]'; is case-sensitive. SELECT * FROM users WHERE LOWER(email) LIKE '[e-mail]'; mismatches case in pattern.

4. Final Answer:

   SELECT * FROM users WHERE UPPER(email) LIKE '[e-mail]'; -> Option C

5. Quick Check:

   Match cases on both sides using UPPER or LOWER [OK]

Hint: Match cases on both sides with UPPER or LOWER [OK]

Common Mistakes:

• Not matching case of pattern and column
• Assuming LIKE is case-insensitive by default
• Mixing LOWER with uppercase pattern