How to fix ERROR 1055: Column isn't in GROUP BY in MySQL

The error message indicates which expression is problematic. For example:

SELECT customer_id, customer_name, COUNT(*) 
FROM orders 
GROUP BY customer_id;

MySQL will report that customer_name is not in GROUP BY. Look at the column positions or names in your SELECT clause.

Include every column in the SELECT list that isn't wrapped in an aggregate function (SUM, COUNT, MAX, AVG, etc.) into the GROUP BY clause:

-- Before (ERROR)
SELECT customer_id, customer_name, COUNT(*) 
FROM orders 
GROUP BY customer_id;

-- After (FIXED)
SELECT customer_id, customer_name, COUNT(*) 
FROM orders 
GROUP BY customer_id, customer_name;

This is the most correct solution as it makes your query intent explicit and guarantees deterministic results.

If you need a column that's not grouped, wrap it in an aggregate function like MAX(), MIN(), GROUP_CONCAT(), or ANY_VALUE():

-- Using MAX to get one value per group
SELECT customer_id, MAX(customer_name), COUNT(*) 
FROM orders 
GROUP BY customer_id;

-- Using GROUP_CONCAT to see all values
SELECT customer_id, GROUP_CONCAT(customer_name), COUNT(*) 
FROM orders 
GROUP BY customer_id;

Choose the function that makes sense for your data. MAX() works if you just need any value; GROUP_CONCAT() works if you need to see all values concatenated.

If you know a column is functionally dependent on your GROUP BY columns (e.g., email uniquely identifies a customer), use ANY_VALUE() to tell MySQL you accept an arbitrary value:

SELECT customer_id, ANY_VALUE(email), COUNT(*) 
FROM orders 
GROUP BY customer_id;

ANY_VALUE() explicitly documents that you understand the risks and are intentionally picking one arbitrary value per group.

Verify which SQL mode is active:

-- Check session SQL mode
SELECT @@sql_mode;

-- Check global SQL mode
SELECT @@GLOBAL.sql_mode;

You should see ONLY_FULL_GROUP_BY in the output if this mode is enabled. Understanding your SQL mode helps identify if this was a recent change after upgrading MySQL.

If you need a quick fix for a single session (not recommended for production):

-- Temporarily disable for current session only
SET sql_mode = (SELECT REPLACE(@@sql_mode, 'ONLY_FULL_GROUP_BY', ''));

-- Then run your query
SELECT customer_id, customer_name, COUNT(*) 
FROM orders 
GROUP BY customer_id;

This is a temporary workaround and does NOT solve the underlying query logic issue. Results may become non-deterministic.

To disable globally, edit your MySQL configuration file (my.cnf or my.ini):

[mysqld]
sql_mode = ""

Then restart MySQL:

# Linux/Mac
sudo systemctl restart mysql

# Or
sudo /usr/local/mysql/support-files/mysql.server restart

WARNING: Disabling this mode removes important validation and can lead to non-deterministic, unpredictable query results that vary based on storage engine or query optimizer changes.