MySQL FIND_IN_SET: Usage, Precautions & Search Method Differences

1. Introduction

Challenges in Searching Comma-Separated Data in MySQL

What is the FIND_IN_SET Function?

SELECT * FROM users WHERE FIND_IN_SET('3', favorite_ids);

Purpose of This Article and Target Readers

• Web engineers and backend developers who use MySQL daily
• Those who need to work with existing systems handling comma-separated data
• SQL beginners struggling with partial matching search methods for data

2. Basic Syntax and Behavior of the FIND_IN_SET Function

Syntax of FIND_IN_SET

FIND_IN_SET(search_value, comma_separated_string)

SELECT FIND_IN_SET('3', '1,2,3,4'); -- Result: 3

Return Value Rules

Example of Use (Returning Position)

SELECT FIND_IN_SET('b', 'a,b,c'); -- Result: 2

Example of Use (When Value Does Not Exist)

SELECT FIND_IN_SET('d', 'a,b,c'); -- Result: 0

Example of Use (When NULL is Included)

SELECT FIND_IN_SET(NULL, 'a,b,c'); -- Result: NULL

Example of Use in WHERE Clause

SELECT * FROM users WHERE FIND_IN_SET('admin', roles);

Notes on Numbers and Strings

SELECT FIND_IN_SET(3, '1,2,3,4');     -- Result: 3
SELECT FIND_IN_SET('3', '1,2,3,4');   -- Result: 3

3. Practical Usage Examples

Searching in Columns with Comma-Separated Strings

SELECT * FROM users WHERE FIND_IN_SET('3', favorite_ids);

It Works Fine Even with Numeric Types

-- OK
SELECT * FROM users WHERE FIND_IN_SET('5', favorite_ids);

-- It works but not strictly recommended
SELECT * FROM users WHERE FIND_IN_SET(5, favorite_ids);

Dynamic Searches (Placeholders or Variables)

SET @target_id = '3';
SELECT * FROM users WHERE FIND_IN_SET(@target_id, favorite_ids);

Tips for Searching Multiple Values

SELECT * FROM users
WHERE FIND_IN_SET('3', favorite_ids) OR FIND_IN_SET('4', favorite_ids);

4. Comparison of FIND_IN_SET Function with Other Search Methods

Commonly Compared Search Methods: IN Clause and LIKE Clause

Comparison with IN Clause

-- Example of IN clause (this does not search for records where favorite_ids matches "3")
SELECT * FROM users WHERE favorite_ids IN ('3');

SELECT * FROM users WHERE FIND_IN_SET('3', favorite_ids);

• IN clause: Use with normalized tables (e.g., SELECT * FROM posts WHERE category_id IN (1, 3, 5))
• FIND_IN_SET: Use with denormalized comma-separated strings

Comparison with LIKE Clause

-- Example of a common mistake with LIKE clause
SELECT * FROM users WHERE favorite_ids LIKE '%3%';

• LIKE clause: Effective for fuzzy string searches but cannot recognize value delimiters
• FIND_IN_SET: Can accurately confirm matches for standalone values within comma-separated lists

Differences from a Performance Perspective

5. Precautions and Best Practices

Values Containing Commas Are Not Supported

Example of What Not to Do:

SELECT FIND_IN_SET('1,2', '1,2,3,4'); -- Result: 1

Performance Issues

Workarounds:

• Instead of comma-separated data, normalize the relations and manage them in a separate table.
• In performance-critical environments, consider temporary table expansion or JOIN strategies.

SELECT users.*
FROM users
JOIN user_favorites ON users.id = user_favorites.user_id
WHERE user_favorites.favorite_id = 3;

From the Perspective of Readability and Maintainability

• The query is not intuitive (it returns positions)
• Adding or removing values is difficult
• It is hard to ensure data integrity (by putting multiple meanings in one column)

When You Absolutely Need to Use FIND_IN_SET

• Apply filters first to reduce the number of search targets
• Prevent string formatting errors (double commas or leading/trailing spaces)
• If possible, perform auxiliary processing on the application side

6. Frequently Asked Questions (FAQ)

Can the FIND_IN_SET function use indexes?

Will it work correctly even if numbers and strings are mixed?

SELECT FIND_IN_SET(3, '1,2,3,4');     -- Result: 3
SELECT FIND_IN_SET('3', '1,2,3,4');   -- Result: 3

Is there a way to search for multiple values at once?

SELECT * FROM users
WHERE FIND_IN_SET('3', favorite_ids)
   OR FIND_IN_SET('4', favorite_ids);

Using FIND_IN_SET degrades performance. What are the countermeasures?

• Switch to a normalized table design
• Apply filter conditions first to limit the search targets
• Use it only limitedly when the data volume is small
• Consider migrating to more structured data representations such as full-text search or JSON type

Will FIND_IN_SET become deprecated in the future?

7. Summary

Reconfirming the Features and Advantages of FIND_IN_SET

Precautions When Using

• Indexes do not work (= searches become slow)
• Not compatible with values containing commas
• Assumes a non-normalized structure
• Can only search for a single value (for multiple searches, OR conditions are required)

When to Use It and When Not To

How to Apply in Practice

• Know it as a technique for flexibly responding assuming the existing DB structure
• Use it as a basis for deciding to adopt normalized data design in the future
• Rather than using it as a temporary fix, accurately understand “what this function is doing”