REPLACE function in SQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this REPLACE function query?

Given the string 'hello world', what will be the result of this SQL query?

SELECT REPLACE('hello world', 'world', 'SQL') AS result;

SQL

SELECT REPLACE('hello world', 'world', 'SQL') AS result;

A 'hello SQL'

B 'hello world'

C 'SQL world'

D 'helloSQL'

💡 Hint

REPLACE changes all occurrences of the second string with the third string inside the first string.

The REPLACE function looks for 'world' in 'hello world' and replaces it with 'SQL', resulting in 'hello SQL'.

❓ query_result

intermediate

What does this REPLACE query return?

What is the output of this SQL query?

SELECT REPLACE('banana', 'a', 'o') AS result;

SQL

SELECT REPLACE('banana', 'a', 'o') AS result;

A 'bnn'

B 'banana'

C 'bonono'

D 'banano'

💡 Hint

Every 'a' in 'banana' is replaced by 'o'.

The REPLACE function replaces all 'a' characters with 'o', so 'banana' becomes 'bonono'.

📝 Syntax

advanced

Which query will cause a syntax error?

Identify which of these SQL queries using REPLACE will cause a syntax error.

A SELECT REPLACE('test', 't', 'T') AS result;

B SELECT REPLACE('test', 't') AS result;

C SELECT REPLACE('test', 't', 'T', 'extra') AS result;

D ;tluser SA )'T' ,'t' ,'tset'(ECALPER TCELES

💡 Hint

REPLACE requires exactly three arguments: the string, the substring to find, and the substring to replace with.

Option B has only two arguments, which is invalid syntax for REPLACE. Options A and B are correct syntax. Option B has too many arguments and will also cause an error, but the question asks for one correct answer causing syntax error, and D is the invalid with missing argument.

🔧 Debug

advanced

Why does this REPLACE query return the original string?

Consider this query:

SELECT REPLACE('apple', 'b', 'c') AS result;

Why does it return 'apple' unchanged?

SQL

SELECT REPLACE('apple', 'b', 'c') AS result;

A Because the function is case-sensitive and 'B' is different from 'b'.

B Because REPLACE only works with numeric strings.

C Because the third argument must be longer than the second.

D Because 'b' is not found in 'apple', so no replacement happens.

💡 Hint

Think about what happens if the substring to replace is not found.

If the substring to replace is not found in the original string, REPLACE returns the original string unchanged.

🧠 Conceptual

expert

How many replacements occur in this query?

Given the string 'abracadabra', how many characters will be replaced by this query?

SELECT REPLACE('abracadabra', 'a', 'x') AS result;

SQL

SELECT REPLACE('abracadabra', 'a', 'x') AS result;

A 5

B 4

C 3

D 6

💡 Hint

Count how many times 'a' appears in 'abracadabra'.

'abracadabra' contains 5 'a' characters, so 5 replacements occur.

Practice

1. What does the SQL REPLACE function do?

easy

A. It converts all characters in a string to uppercase.

B. It deletes a substring from a string without replacement.

C. It extracts a substring from a string based on position.

D. It replaces all occurrences of a specified substring within a string with another substring.

Solution

1. Step 1: Understand the purpose of REPLACE

   The REPLACE function is designed to find all instances of a substring in a string and swap them with another substring.

2. Step 2: Compare with other string functions

   Unlike deleting or extracting substrings, REPLACE changes the content by substitution.

3. Final Answer:

   It replaces all occurrences of a specified substring within a string with another substring. -> Option D

4. Quick Check:

   REPLACE swaps substrings = A [OK]

Hint: REPLACE swaps all target text with new text [OK]

Common Mistakes:

• Thinking REPLACE deletes text without substitution
• Confusing REPLACE with substring extraction
• Assuming REPLACE changes case of text

2. Which of the following is the correct syntax for the SQL REPLACE function?

easy

A. REPLACE(string, old_substring, new_substring)

B. REPLACE(old_substring, new_substring, string)

C. REPLACE(string, new_substring, old_substring)

D. REPLACE(new_substring, string, old_substring)

Solution

1. Step 1: Recall REPLACE function parameter order

   The correct order is the original string first, then the substring to replace, then the new substring.

2. Step 2: Verify each option

   Only REPLACE(string, old_substring, new_substring) follows the correct order: REPLACE(string, old_substring, new_substring).

3. Final Answer:

   REPLACE(string, old_substring, new_substring) -> Option A

4. Quick Check:

   Correct parameter order = D [OK]

Hint: Remember: original string first, then old, then new substring [OK]

Common Mistakes:

• Swapping old and new substring positions
• Putting new substring before old substring
• Confusing parameter order

3. Given the SQL query:
SELECT REPLACE('banana', 'a', 'o');
What is the output?

medium

A. 'bnn'

B. 'banana'

C. 'bonono'

D. 'banano'

Solution

1. Step 1: Identify the string and substrings

   The original string is 'banana'. We replace all 'a' with 'o'.

2. Step 2: Replace all 'a' with 'o'

   Replacing each 'a' in 'banana' results in 'bonono'.

3. Final Answer:

   'bonono' -> Option C

4. Quick Check:

   All 'a' replaced by 'o' = 'bonono' [OK]

Hint: Replace every target letter, not just first [OK]

Common Mistakes:

• Replacing only first occurrence
• Not replacing any character
• Removing characters instead of replacing

4. What is wrong with this SQL query?
SELECT REPLACE('hello world', 'l');

medium

A. It is missing the new substring to replace with.

B. The string to search in is missing.

C. The REPLACE function cannot be used in SELECT statements.

D. The function should be written as REPLACE('l', 'hello world').

Solution

1. Step 1: Check REPLACE function parameters

   REPLACE requires three parameters: original string, old substring, new substring.

2. Step 2: Identify missing parameter

   The query only has two parameters: original string and old substring. The new substring is missing.

3. Final Answer:

   It is missing the new substring to replace with. -> Option A

4. Quick Check:

   Missing third parameter = A [OK]

Hint: REPLACE needs 3 parameters: string, old, new [OK]

Common Mistakes:

• Using only two parameters
• Swapping parameter order
• Assuming REPLACE works with one substring only

5. You have a table products with a column description containing the text 'color' spelled as 'colour' in some rows. Which SQL query correctly updates all 'colour' to 'color' in the description column?

hard

A. UPDATE products SET description = REPLACE('colour', 'color', description);

B. UPDATE products SET description = REPLACE(description, 'colour', 'color');

C. UPDATE products SET description = REPLACE(description, 'color', 'colour');

D. UPDATE products SET description = REPLACE(description, 'colour');

Solution

1. Step 1: Understand the goal

   We want to replace all occurrences of 'colour' with 'color' in the description column.

2. Step 2: Check each query's correctness

   UPDATE products SET description = REPLACE(description, 'colour', 'color'); correctly uses REPLACE with the column first, then old substring 'colour', then new substring 'color'. UPDATE products SET description = REPLACE('colour', 'color', description); has wrong parameter order. UPDATE products SET description = REPLACE(description, 'color', 'colour'); replaces 'color' with 'colour' (opposite). UPDATE products SET description = REPLACE(description, 'colour'); misses the new substring parameter.

3. Final Answer:

   UPDATE products SET description = REPLACE(description, 'colour', 'color'); -> Option B

4. Quick Check:

   Correct update syntax with REPLACE = B [OK]

Hint: Use REPLACE(column, old, new) in UPDATE to fix text [OK]

Common Mistakes:

• Swapping old and new substrings
• Missing new substring parameter
• Using wrong parameter order