Illegal mix of collations (utf8mb4_unicode_ci,EXPLICIT) and (utf8_general_ci,COERCIBLE) for operation '='

Question

Alright, I give up. I'm 2 days into this error and I need help.

Disclaimer: I will need help improving this question and will try to do a good job of describing the issue at hand, what I have done so far to address the issue, and share blog posts and the documentation that I have read in search of a solution.

The Question (also, asked below in context):

So the question is, why does the same query behave differently when run from Rails instead of from the mysql command line? Specifically, where is "(utf8_general_ci,COERCIBLE)" coming from?

The Problem: Autoresponder.find_by(keyword: '😕') fails with the following error:

ActiveRecord::StatementInvalid: Mysql2::Error: Illegal mix of collations 
(utf8mb4_unicode_ci,IMPLICIT) and (utf8_general_ci,COERCIBLE) 
for operation '=': 
SELECT  `autoresponders`.* 
FROM `autoresponders`  
WHERE `autoresponders`.`keyword` = '😕' 
LIMIT 1

Autoresponder is a model that has the attribute keyword

I read that I needed to specify my collation. So I tested out the following code:

Autoresponder.where('keyword collate utf8mb4_unicode_ci = ?', '😕')

and got the following error:

Illegal mix of collations 
(utf8mb4_unicode_ci,EXPLICIT) and (utf8_general_ci,COERCIBLE) 
for operation '=': 
SELECT `autoresponders`.* 
FROM `autoresponders`  
WHERE (keyword collate utf8mb4_unicode_ci = '😕')

All that did was change the collation from IMPLICIT to EXPLICIT.

I tried running the query in Sequel Pro and it worked (with and without the collate keyword). For clarity's sake here's the query:

SELECT `autoresponders`.* 
FROM `autoresponders`  
WHERE (keyword collate utf8mb4_unicode_ci = '😕');

SELECT `autoresponders`.* 
FROM `autoresponders`  
WHERE (keyword = '😕 ');

AND it works! The queries ran without errors. I also ran mysql and was able to run the query there too. But I noticed something when I pasted the query into the mysql command line. It automatically used the Unicode name for the character instead of the actual character. Here is the query as observed in the mysql command line:

SELECT `autoresponders`.* 
FROM `autoresponders`  
WHERE (keyword collate utf8mb4_unicode_ci ='\U+1F615');

This query works.

So the question is, why does the same query fail in Rails but work in Sequel Pro? Specifically, where is "(utf8_general_ci,COERCIBLE)" coming from, and how do I fix this mess?

I thought that it might be coming from ActiveRecord, but running ActiveRecord::Base.connection.collation in rails console returns utf8mb4_unicode_ci

Here are my db character encoding and collation variables (and the query that retrieved them).

SHOW VARIABLES WHERE Variable_name LIKE 'character\_set\_%' OR Variable_name LIKE 'collation%';
character_set_client        utf8mb4
character_set_connection    utf8mb4
character_set_database      utf8mb4
character_set_filesystem    binary
character_set_results       utf8mb4
character_set_server        latin1
character_set_system        utf8
collation_connection        utf8mb4_unicode_ci
collation_database          utf8mb4_unicode_ci
collation_server            latin1_swedish_ci

Here is the create syntax for the Autorsponders table:

CREATE TABLE `autoresponders` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `keyword` varchar(191) COLLATE utf8mb4_unicode_ci DEFAULT '',
  `body` varchar(191) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  `created_at` datetime DEFAULT NULL,
  `updated_at` datetime DEFAULT NULL,
  `provisioned_number_id` int(11) DEFAULT NULL,
  `outgoing_provisioned_number_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci ROW_FORMAT=DYNAMIC;

Context: Rails 4.0.13, Mysql version 5.6.22-1+deb.sury.org~precise+1-log

Here are some blog posts and SO articles that I have read so far: https://mathiasbynens.be/notes/mysql-utf8mb4

http://airbladesoftware.com/notes/fixing-mysql-illegal-mix-of-collations/

Is "SET CHARACTER SET utf8" necessary?

Illegal mix of collations (utf8_unicode_ci,IMPLICIT) and (utf8_general_ci,IMPLICIT) for operation '='

Not case sensitive search with active record

https://dev.mysql.com/doc/refman/5.0/en/server-system-variables.html#sysvar_collation_server

All of this led me to create this meme:

Sincerely,

An exhausted fellow developer.

Thanks.

Answer 1

I met similar problem and solved finally. At first, my MySQL conf is：

character-set-server = utf8
collation-server     = utf8_general_ci

One day, i found that emoji could be saved correctly only with utf8mb4, so i change the specified column's character set and collation like this:

  `nickname` varchar(100) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci,

By now, everything still fine, data could be saved and display correctly by java web application.

but when i query data like

SELECT * FROM table_name WHERE nickname LIKE '%😈%';

error raises.

Finally i changed mysql conf to

character-set-server = utf8mb4
collation-server     = utf8mb4_unicode_ci

and everything goes fine.

Here is a screenshot of mysql client, notice the nickname attribute