REPLACE function in MySQL

Introduction

The REPLACE function helps you change parts of text inside your data easily.

You want to fix a typo in many text entries at once.

You need to update old words to new ones in a list of names.

You want to remove unwanted characters from a text field.

You want to change a part of an address or email in your database.

Syntax

MySQL

REPLACE(original_text, text_to_find, text_to_replace_with)

It looks inside the original_text and replaces all occurrences of text_to_find.

If text_to_find is not found, the original_text stays the same.

Examples

Replaces 'world' with 'friend' in the text.

MySQL

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

Changes all 'a's to 'o's, resulting in 'bonono'.

MySQL

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

No 'x' found, so the text stays 'apple'.

MySQL

SELECT REPLACE('apple', 'x', 'y');

Sample Program

This replaces every 'cats' with 'dogs' in the sentence.

MySQL

SELECT REPLACE('I love cats and cats love me', 'cats', 'dogs') AS result;

Important Notes

REPLACE is case-sensitive, so 'Cats' and 'cats' are different.

It replaces all matches, not just the first one.

Use it carefully when replacing common words to avoid unwanted changes.

Summary

REPLACE changes parts of text inside strings.

It replaces all occurrences of the text you want to change.

If the text to find is missing, the original text stays unchanged.

Practice

1. What does the REPLACE function do in MySQL?

easy

A. It deletes the entire string if a substring is found.

B. It splits the string into multiple parts.

C. It adds a substring at the end of the string.

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

Solution

1. Step 1: Understand the purpose of REPLACE

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

2. Step 2: Compare options with the function behavior

   Only It replaces all occurrences of a specified substring within a string. correctly describes this behavior. Options A, C, and D describe different string operations.

3. Final Answer:

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

4. Quick Check:

   REPLACE changes parts of text inside strings = B [OK]

Hint: REPLACE swaps all found text parts inside a string [OK]

Common Mistakes:

• Thinking REPLACE deletes the whole string
• Confusing REPLACE with string splitting
• Assuming REPLACE adds text instead of replacing

2. Which of the following is the correct syntax to replace 'cat' with 'dog' in the string 'catapult' using MySQL?

easy

A. REPLACE('catapult', 'cat', 'dog')

B. REPLACE('catapult', 'dog', 'cat')

C. REPLACE('catapult', 'catapult', 'dog')

D. REPLACE('catapult', 'dog', 'dog')

Solution

1. Step 1: Recall REPLACE syntax

   The syntax is REPLACE(original_string, string_to_find, string_to_replace_with).

2. Step 2: Match parameters to the question

   We want to replace 'cat' with 'dog' in 'catapult', so the correct call is REPLACE('catapult', 'cat', 'dog').

3. Final Answer:

   REPLACE('catapult', 'cat', 'dog') -> Option A

4. Quick Check:

   REPLACE(original, find, replace) = A [OK]

Hint: Syntax is REPLACE(text, find, replace) always [OK]

Common Mistakes:

• Swapping find and replace arguments
• Replacing the whole string instead of substring
• Using wrong order of parameters

3. What is the result of this query?

SELECT REPLACE('hello world', 'l', 'x');

medium

A. 'hello world'

B. 'hexxo worlx'

C. 'hexxo worxd'

D. 'hexxo worll'

Solution

1. Step 1: Identify what is replaced

   All occurrences of 'l' in 'hello world' are replaced with 'x'.

2. Step 2: Perform the replacement

   'hello world' becomes 'hexxo worlx' because every 'l' changes to 'x'.

3. Final Answer:

   'hexxo worlx' -> Option B

4. Quick Check:

   Replace all 'l' with 'x' = 'hexxo worlx' [OK]

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

Common Mistakes:

• Replacing only first occurrence
• Not replacing at all
• Replacing wrong characters

4. Identify the error in this query:

SELECT REPLACE('database', 'a');

medium

A. Missing third argument for replacement string.

B. The first argument should be a column name, not a string.

C. REPLACE cannot be used in SELECT statements.

D. The function name should be REPLACESTR.

Solution

1. Step 1: Check REPLACE function arguments

   REPLACE requires three arguments: original string, string to find, and string to replace with.

2. Step 2: Identify missing argument

   The query only has two arguments, missing the replacement string.

3. Final Answer:

   Missing third argument for replacement string. -> Option A

4. Quick Check:

   REPLACE needs 3 arguments = A [OK]

Hint: REPLACE needs 3 arguments: original, find, replace [OK]

Common Mistakes:

• Forgetting the replacement string
• Using wrong function name
• Thinking REPLACE can't be in SELECT

5. Given a table products with a column code containing values like 'AB-123', 'AB-456', and 'CD-789', which query replaces the prefix 'AB-' with 'XY-' only in the code column?

hard

A. SELECT REPLACE(code, 'AB', 'XY') AS new_code FROM products;

B. SELECT REPLACE('code', 'AB-', 'XY-') AS new_code FROM products;

C. SELECT REPLACE(code, 'AB-', 'XY-') AS new_code FROM products;

D. SELECT REPLACE(code, 'XY-', 'AB-') AS new_code FROM products;

Solution

1. Step 1: Understand the goal

   We want to replace the prefix 'AB-' with 'XY-' in the column code values.

2. Step 2: Analyze each option

   SELECT REPLACE(code, 'AB-', 'XY-') AS new_code FROM products; correctly uses REPLACE on the column code replacing 'AB-' with 'XY-'. SELECT REPLACE('code', 'AB-', 'XY-') AS new_code FROM products; treats 'code' as a string literal, not a column. SELECT REPLACE(code, 'XY-', 'AB-') AS new_code FROM products; reverses replacement. SELECT REPLACE(code, 'AB', 'XY') AS new_code FROM products; replaces 'AB' without the dash, which may affect unintended parts.

3. Final Answer:

   SELECT REPLACE(code, 'AB-', 'XY-') AS new_code FROM products; -> Option C

4. Quick Check:

   Replace prefix 'AB-' with 'XY-' in column = D [OK]

Hint: Use column name as first argument, exact substring to replace [OK]

Common Mistakes:

• Using quotes around column name
• Replacing wrong substring
• Swapping find and replace strings