UPPER, LOWER, INITCAP in PostgreSQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this UPPER function?

Given the following SQL query, what will be the output?

PostgreSQL

SELECT UPPER('Hello World!') AS result;

A hello world!

B HELLO WORLD!

C Hello World!

D hELLO wORLD!

💡 Hint

UPPER converts all letters to uppercase.

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

❓ query_result

intermediate

What does LOWER do to mixed case text?

What is the output of this query?

PostgreSQL

SELECT LOWER('PostgreSQL Is Fun!') AS result;

A postgresql is fun!

B pOSTGRESql iS fUN!

C POSTGRESQL IS FUN!

D PostgreSQL Is Fun!

💡 Hint

LOWER converts all letters to lowercase.

The LOWER function converts all letters in the string to lowercase letters.

❓ query_result

advanced

How does INITCAP format this sentence?

What will be the output of this query?

PostgreSQL

SELECT INITCAP('welcome to the world of SQL') AS result;

A Welcome To The World Of Sql

B WELCOME TO THE WORLD OF SQL

C welcome to the world of sql

D Welcome to the world of SQL

💡 Hint

INITCAP capitalizes the first letter of each word.

The INITCAP function capitalizes the first letter of each word and makes the rest lowercase.

🧠 Conceptual

advanced

Which function would you use to make a case-insensitive search?

You want to find all rows where the column name matches 'alice' regardless of case. Which function is best to use in the WHERE clause?

A WHERE INITCAP(name) = 'Alice'

B WHERE LOWER(name) = 'ALICE'

C WHERE UPPER(name) = 'ALICE'

D WHERE name = 'alice'

💡 Hint

Think about converting both sides to the same case.

Using UPPER(name) = 'ALICE' converts the column to uppercase and compares it to uppercase 'ALICE', making the search case-insensitive.

📝 Syntax

expert

What error does this query raise?

Consider this query: SELECT INITCAP(12345) AS result; What error will PostgreSQL raise?

A ERROR: syntax error at or near "12345"

B ERROR: invalid input syntax for type integer

C No error, returns '12345'

D ERROR: function initcap(integer) does not exist

💡 Hint

INITCAP expects a string input, not a number.

The INITCAP function requires a string argument. Passing an integer causes PostgreSQL to report that the function with integer argument does not exist.

Practice

1. What does the UPPER function do to a text string in PostgreSQL?

easy

A. Reverses the string

B. Converts all letters to lowercase

C. Capitalizes only the first letter of the string

D. Converts all letters to uppercase

Solution

1. Step 1: Understand the UPPER function

   The UPPER function changes every letter in the input text to its uppercase form.

2. Step 2: Compare with other options

   LOWER converts to lowercase, INITCAP capitalizes first letters, reversing is unrelated.

3. Final Answer:

   Converts all letters to uppercase -> Option D

4. Quick Check:

   UPPER = all uppercase [OK]

Hint: UPPER means all letters become capital [OK]

Common Mistakes:

• Confusing UPPER with LOWER
• Thinking INITCAP only changes first letter of whole string
• Assuming UPPER reverses text

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

easy

A. SELECT LOWER name FROM table;

B. SELECT LOWER(name);

C. SELECT LOWER(name) FROM table;

D. SELECT name.LOWER() FROM table;

Solution

1. Step 1: Check function call syntax

   In PostgreSQL, functions are called with parentheses around arguments, e.g., LOWER(name).

2. Step 2: Validate full query syntax

   SELECT LOWER(name) FROM table; correctly uses SELECT LOWER(name) FROM table; which is valid SQL syntax.

3. Final Answer:

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

4. Quick Check:

   Function call syntax = LOWER(name) [OK]

Hint: Use parentheses for functions: LOWER(column) [OK]

Common Mistakes:

• Omitting parentheses after function name
• Using dot notation like name.LOWER() which is invalid
• Missing FROM clause in query

3. Given a table users with a column fullname containing 'john DOE', what is the output of the query SELECT INITCAP(fullname) FROM users;?

medium

A. 'John Doe'

B. 'John DOE'

C. 'John doe'

D. 'JOHN DOE'

Solution

1. Step 1: Understand INITCAP behavior

   INITCAP capitalizes the first letter of each word and makes the rest lowercase.

2. Step 2: Apply to 'john DOE'

   It converts 'john' to 'John' and 'DOE' to 'Doe'.

3. Final Answer:

   'John Doe' -> Option A

4. Quick Check:

   INITCAP('john DOE') = 'John Doe' [OK]

Hint: INITCAP capitalizes first letter of each word [OK]

Common Mistakes:

• Assuming INITCAP only changes first word
• Thinking it keeps uppercase letters as is
• Confusing with UPPER or LOWER functions

4. Identify the error in this query: SELECT INITCAP fullname FROM employees;

medium

A. Column name should be uppercase

B. Missing parentheses around column name

C. Missing FROM clause

D. INITCAP is not a valid function

Solution

1. Step 1: Check function syntax

   Functions require parentheses around their arguments, so INITCAP should be called as INITCAP(fullname).

2. Step 2: Verify other parts

   FROM clause is present, INITCAP is valid, column case does not matter.

3. Final Answer:

   Missing parentheses around column name -> Option B

4. Quick Check:

   Function call needs parentheses [OK]

Hint: Always use parentheses with functions [OK]

Common Mistakes:

• Omitting parentheses for function calls
• Thinking column names must be uppercase
• Confusing missing FROM clause error

5. You want to display a list of product names from the products table where each word in the product name starts with a capital letter, but the rest of the letters are lowercase. Which query achieves this?

hard

A. SELECT INITCAP(product_name) FROM products;

B. SELECT UPPER(product_name) FROM products;

C. SELECT LOWER(product_name) FROM products;

D. SELECT CONCAT(UPPER(SUBSTRING(product_name,1,1)), LOWER(SUBSTRING(product_name,2))) FROM products;

Solution

1. Step 1: Understand the requirement

   Each word's first letter capitalized and rest lowercase matches INITCAP behavior.

2. Step 2: Evaluate options

   The INITCAP option does exactly this. The UPPER option makes all uppercase, the LOWER option makes all lowercase, the CONCAT option only capitalizes first letter of whole string.

3. Final Answer:

   SELECT INITCAP(product_name) FROM products; -> Option A

4. Quick Check:

   INITCAP = capitalized words [OK]

Hint: Use INITCAP for capitalizing each word [OK]

Common Mistakes:

• Using UPPER or LOWER instead of INITCAP
• Trying to manually concatenate substrings for each word
• Assuming INITCAP only affects first word