REPLACE function in SQL

Introduction

The REPLACE function helps you change parts of text inside your data. It swaps old words or letters with new ones.

You want to fix a typo in many records at once.

You need to update a product code by changing some characters.

You want to remove unwanted characters from a text field.

You want to change a domain name in email addresses.

You want to replace spaces with underscores in usernames.

Syntax

SQL

REPLACE(original_string, string_to_find, string_to_replace_with)

The function looks for all occurrences of string_to_find inside original_string and replaces them.

If string_to_find is not found, the original_string is returned unchanged.

Examples

This changes 'world' to 'SQL' resulting in 'hello SQL'.

SQL

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

This replaces dashes with slashes in a date string.

SQL

SELECT REPLACE('2023-06-01', '-', '/');

This replaces every 'a' with 'o', resulting in 'bonono'.

SQL

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

Sample Program

This query replaces the word 'apples' with 'oranges' in the sentence.

SQL

SELECT REPLACE('I love apples', 'apples', 'oranges') AS fruit_change;

Important Notes

REPLACE is case-sensitive in most SQL databases.

If you want to replace only the first occurrence, you may need other functions or methods.

Summary

REPLACE swaps parts of text inside strings.

It changes all occurrences of the target text.

Useful for fixing or updating text data quickly.

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