How Do I Fix the \'Illegal Mix of Collations\' Error in MySQL?

Illegal Collation Error in MySQL: Resolving the Mix of Collations

The "Illegal mix of collations" error in MySQL arises when comparing values with different character sets or collations. Let's analyze this issue in the context of your query:

<code class="sql">SELECT username, (SUM(rating)/COUNT(*)) as TheAverage, Count(*) as TheCount 
FROM ratings WHERE month='Aug' 
AND username IN (SELECT username FROM users WHERE gender =1)
GROUP BY username HAVING TheCount > 4
ORDER BY TheAverage DESC, TheCount DESC</code>

Upon adding the following line to your query:

<code class="sql">AND username IN (SELECT username FROM users WHERE gender =1)</code>

you encountered the "Illegal mix of collations" error. This is because the username column in the ratings table may have a different collation from the username column in the users table.

Identifying the Incorrect Collations:

To determine which columns are causing the collation conflict, use the following query:

<code class="sql">SELECT table_schema, table_name, column_name, character_set_name, collation_name
FROM information_schema.columns
WHERE collation_name = 'latin1_general_ci'
ORDER BY table_schema, table_name, ordinal_position;</code>

This query will display the tables and columns that have the collation latin1_general_ci.

Resolving the Issue:

To resolve the error, convert the table with the incorrect collation to the required collation, which is typically latin1_swedish_ci. Use the following query:

<code class="sql">ALTER TABLE tbl_name CONVERT TO CHARACTER SET latin1 COLLATE 'latin1_swedish_ci';</code>

where tbl_name is the name of the table with the incorrect collation.

By resolving the collation conflict, the modified query should execute successfully.

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