REPLACE function in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the REPLACE function do in SQL?

The REPLACE function searches for all occurrences of a specified substring in a string and replaces them with another substring.

beginner

Syntax of the REPLACE function in SQL?

REPLACE(original_string, string_to_find, string_to_replace_with)

beginner

Example: What is the result of REPLACE('apple pie', 'pie', 'tart')?

The result is 'apple tart' because 'pie' is replaced by 'tart'.

intermediate

Can REPLACE function change multiple occurrences in a string?

Yes, REPLACE changes all occurrences of the target substring in the original string.

beginner

What happens if the string to find is not present in the original string?

The original string is returned unchanged because there is nothing to replace.

What does REPLACE('banana', 'a', 'o') return?

A bonono

B banana

C bnn

D banano

All 'a' characters are replaced with 'o', so 'banana' becomes 'bonono'.

Which of these is the correct syntax for REPLACE?

A REPLACE(string_to_find, original_string, replacement)

B REPLACE(original_string, string_to_find, replacement)

C REPLACE(replacement, original_string, string_to_find)

D REPLACE(original_string, replacement, string_to_find)

The correct order is original string, string to find, then replacement string.

If REPLACE('hello world', 'x', 'y') is run, what is the output?

A error

B hello yorld

C hello worly

D hello world

Since 'x' is not found, the original string is returned unchanged.

Does REPLACE function modify the original data in the database?

A No, it only returns a modified string without changing stored data

B Yes, it updates the stored data automatically

C Yes, but only if used with UPDATE statement

D No, it deletes the original data

REPLACE returns a new string with replacements; it does not change stored data unless used inside an UPDATE.

Which SQL function would you use to replace text inside a string?

A SUBSTRING

B CONCAT

C REPLACE

D TRIM

REPLACE is used to substitute parts of a string with new text.

Explain how the REPLACE function works in SQL with an example.

Think about how you would change words in a sentence.

What happens if the substring to replace is not found in the original string when using REPLACE?

Consider what happens if you try to replace a word that isn't there.

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