UPPER and LOWER functions in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the UPPER function do in SQL?

The UPPER function converts all letters in a text string to uppercase letters.

beginner

What is the purpose of the LOWER function in SQL?

The LOWER function converts all letters in a text string to lowercase letters.

beginner

Write a SQL query to convert the column 'name' to uppercase.

SELECT UPPER(name) FROM table_name;

intermediate

How can you make a case-insensitive search using UPPER or LOWER?

Convert both the column and the search term to the same case using UPPER or LOWER, then compare them.

beginner

If you apply LOWER to 'Hello World!', what is the result?

The result is 'hello world!'. Only letters change case; punctuation and spaces stay the same.

What will SELECT UPPER('sql') return?

A 'SQL'

B 'sql'

C 'Sql'

D 'sQl'

UPPER converts all letters to uppercase, so 'sql' becomes 'SQL'.

Which function converts text to lowercase in SQL?

A LOWER()

B UPPER()

C LOWCASE()

D DOWN()

LOWER() is the standard SQL function to convert text to lowercase.

How can you compare two strings ignoring case differences?

A Compare strings directly without functions

B Use UPPER on both strings before comparing

C Use UPPER on one string only

D Use LOWER on one string only

Converting both strings to the same case (UPPER or LOWER) ensures case-insensitive comparison.

What happens to numbers and punctuation when using UPPER or LOWER?

A They change to uppercase or lowercase

B They are removed

C They stay the same

D They cause an error

Numbers and punctuation are not affected by UPPER or LOWER functions.

Which SQL function would you use to make 'Hello' into 'hello'?

A UPPER('Hello')

B CAPITALIZE('Hello')

C LOWCASE('Hello')

D LOWER('Hello')

LOWER('Hello') converts all letters to lowercase, resulting in 'hello'.

Explain how UPPER and LOWER functions work in SQL and give an example of each.

Think about changing letter cases in text columns.

Describe a real-life situation where using UPPER or LOWER in SQL would be helpful.

Imagine searching names or emails without worrying about letter case.

Practice

1. What does the SQL function UPPER('Hello World') return?

easy

A. 'Hello World'

B. 'HELLO WORLD'

C. 'hello world'

D. 'HeLLo WoRLD'

Solution

1. Step 1: Understand the UPPER function

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

2. Step 2: Apply UPPER to 'Hello World'

   Converting each letter to uppercase results in 'HELLO WORLD'.

3. Final Answer:

   'HELLO WORLD' -> Option B

4. Quick Check:

   UPPER('Hello World') = 'HELLO WORLD' [OK]

Hint: UPPER makes all letters capital [OK]

Common Mistakes:

• Confusing UPPER with LOWER
• Thinking it changes only first letter
• Assuming it reverses the string

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

easy

A. SELECT LOWER(name) FROM table;

B. SELECT LOWER name FROM table;

C. SELECT name.LOWER() FROM table;

D. SELECT LOWER[name] FROM table;

Solution

1. Step 1: Recall correct function syntax

   The LOWER function is called with parentheses around the column name: LOWER(column_name).

2. Step 2: Check each option

   SELECT LOWER(name) FROM table; uses correct syntax: LOWER(name). Others have syntax errors or invalid notation.

3. Final Answer:

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

4. Quick Check:

   Use LOWER(column) with parentheses [OK]

Hint: Use LOWER(column_name) with parentheses [OK]

Common Mistakes:

• Omitting parentheses
• Using dot notation like name.LOWER()
• Using square brackets inside function

3. Given a table users with a column username containing values: 'Alice', 'BOB', 'charlie', what will the query SELECT LOWER(username) FROM users; return?

medium

A. ['ALICE', 'BOB', 'CHARLIE']

B. ['Alice', 'BOB', 'charlie']

C. ['alice', 'bob', 'charlie']

D. ['aLiCe', 'bOb', 'cHaRlIe']

Solution

1. Step 1: Understand LOWER function effect on each username

   LOWER converts all letters to lowercase regardless of original case.

2. Step 2: Apply LOWER to each username

   'Alice' -> 'alice', 'BOB' -> 'bob', 'charlie' -> 'charlie'.

3. Final Answer:

   ['alice', 'bob', 'charlie'] -> Option C

4. Quick Check:

   LOWER converts all letters to lowercase [OK]

Hint: LOWER makes all letters small [OK]

Common Mistakes:

• Assuming only first letter changes
• Confusing LOWER with UPPER
• Expecting mixed case output

4. Identify the error in this SQL query: SELECT LOWER username FROM users;

medium

A. No error, query is correct

B. LOWER function does not exist

C. Table name is incorrect

D. Missing parentheses around column name

Solution

1. Step 1: Check function syntax

   SQL functions require parentheses around arguments, so LOWER(username) is correct.

2. Step 2: Identify missing parentheses

   The query uses LOWER username without parentheses, causing syntax error.

3. Final Answer:

   Missing parentheses around column name -> Option D

4. Quick Check:

   Functions need parentheses [OK]

Hint: Always use parentheses with functions [OK]

Common Mistakes:

• Omitting parentheses for functions
• Assuming functions work like keywords
• Ignoring syntax errors

5. You want to find all rows in a table products where the category column equals 'Books', ignoring case differences. Which SQL WHERE clause correctly does this?

hard

A. WHERE LOWER(category) = 'books' AND UPPER(category) = 'BOOKS'

B. WHERE category = 'Books'

C. WHERE LOWER(category) = 'Books'

D. WHERE UPPER(category) = 'BOOKS'

Solution

1. Step 1: Understand case-insensitive comparison

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

2. Step 2: Apply LOWER and UPPER to category and compare both

   Using WHERE LOWER(category) = 'books' AND UPPER(category) = 'BOOKS' ensures the category matches 'Books' ignoring case by checking both lowercase and uppercase.

3. Final Answer:

   WHERE LOWER(category) = 'books' AND UPPER(category) = 'BOOKS' -> Option A

4. Quick Check:

   Use both LOWER and UPPER on the column to ensure case-insensitive match [OK]

Hint: Convert both sides to same case for comparison [OK]

Common Mistakes:

• Comparing without case conversion
• Mixing cases in comparison string
• Using only one case function