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

Error message on MySql:

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

I have gone through several other posts and was not able to solve this problem. The part affected is something similar to this:

CREATE TABLE users (
    userID INT UNSIGNED NOT NULL AUTO_INCREMENT,
    firstName VARCHAR(24) NOT NULL,
    lastName VARCHAR(24) NOT NULL,
    username VARCHAR(24) NOT NULL,
    password VARCHAR(40) NOT NULL,
    PRIMARY KEY (userid)
) ENGINE = INNODB CHARACTER SET utf8 COLLATE utf8_unicode_ci;

CREATE TABLE products (
    productID INT UNSIGNED NOT NULL AUTO_INCREMENT,
    title VARCHAR(104) NOT NULL,
    picturePath VARCHAR(104) NULL,
    pictureThumb VARCHAR(104) NULL,
    creationDate DATE NOT NULL,
    closeDate DATE NULL,
    deleteDate DATE NULL,
    varPath VARCHAR(104) NULL,
    isPublic TINYINT(1) UNSIGNED NOT NULL DEFAULT '1',
    PRIMARY KEY (productID)
) ENGINE = INNODB CHARACTER SET utf8 COLLATE utf8_unicode_ci;

CREATE TABLE productUsers (
    productID INT UNSIGNED NOT NULL,
    userID INT UNSIGNED NOT NULL,
    permission VARCHAR(16) NOT NULL,
    PRIMARY KEY (productID,userID),
    FOREIGN KEY (productID) REFERENCES products (productID) ON DELETE RESTRICT ON UPDATE NO ACTION,
    FOREIGN KEY (userID) REFERENCES users (userID) ON DELETE RESTRICT ON UPDATE NO ACTION
) ENGINE = INNODB CHARACTER SET utf8 COLLATE utf8_unicode_ci;

The stored procedure I'm using is this:

CREATE PROCEDURE updateProductUsers (IN rUsername VARCHAR(24),IN rProductID INT UNSIGNED,IN rPerm VARCHAR(16))
BEGIN
    UPDATE productUsers
        INNER JOIN users
        ON productUsers.userID = users.userID
        SET productUsers.permission = rPerm
        WHERE users.username = rUsername
        AND productUsers.productID = rProductID;
END

I was testing with php, but the same error is given with SQLyog. I have also tested recreating the entire DB but to no good.

Any help will be much appreciated.

I had a similar problem, but it occurred to me inside procedure, when my query param was set using variable e.g. SET @value='foo'.

What was causing this was mismatched collation_connection and Database collation. Changed collation_connection to match collation_database and problem went away. I think this is more elegant approach than adding COLLATE after param/value.

To sum up: all collations must match. Use SHOW VARIABLES and make sure collation_connection and collation_database match (also check table collation using SHOW TABLE STATUS [table_name]).

Answer is adding to @Sebas' answer - setting the collation of my local environment. Do not try this on production.

ALTER DATABASE databasename CHARACTER SET utf8 COLLATE utf8_unicode_ci;

ALTER TABLE tablename CONVERT TO CHARACTER SET utf8 COLLATE utf8_unicode_ci;

Source of this solution

A bit similar to @bpile answer, my case was a my.cnf entry setting collation-server = utf8_general_ci. After I realized that (and after trying everything above), I forcefully switched my database to utf8_general_ci instead of utf8_unicode_ci and that was it:

ALTER DATABASE `db` CHARACTER SET utf8 COLLATE utf8_general_ci;

In my own case I have the following error

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

$this->db->select("users.username as matric_no, CONCAT(users.surname, ' ', users.first_name, ' ', users.last_name) as fullname") ->join('users', 'users.username=classroom_students.matric_no', 'left') ->where('classroom_students.session_id', $session) ->where('classroom_students.level_id', $level) ->where('classroom_students.dept_id', $dept);

After weeks of google searching I noticed that the two fields I am comparing consists of different collation name. The first one i.e username is of utf8_general_ci while the second one is of utf8_unicode_ci so I went back to the structure of the second table and changed the second field (matric_no) to utf8_general_ci and it worked like a charm.

This happens where a column is explicitly set to a different collation or the default collation is different in the table queried.

if you have many tables you want to change collation on run this query:

select concat('ALTER TABLE ', t.table_name , ' CONVERT TO CHARACTER 
SET utf8 COLLATE utf8_unicode_ci;') from (SELECT table_name FROM 
information_schema.tables where table_schema='SCHRMA') t;

this will output the queries needed to convert all the tables to use the correct collation per column

I spent half a day searching for answers to an identical "Illegal mix of collations" error with conflicts between utf8_unicode_ci and utf8_general_ci.

I found that some columns in my database were not specifically collated utf8_unicode_ci. It seems mysql implicitly collated these columns utf8_general_ci.

Specifically, running a 'SHOW CREATE TABLE table1' query outputted something like the following:

| table1 | CREATE TABLE `table1` (
`id` int(11) NOT NULL,
`col1` varchar(4) CHARACTER SET utf8 NOT NULL,
`col2` int(11) NOT NULL,
PRIMARY KEY (`col1`,`col2`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci |

Note the line 'col1' varchar(4) CHARACTER SET utf8 NOT NULL does not have a collation specified. I then ran the following query:

ALTER TABLE table1 CHANGE col1 col1 VARCHAR(4) CHARACTER SET utf8 COLLATE utf8_unicode_ci NOT NULL;

This solved my "Illegal mix of collations" error. Hope this might help someone else out there.

Despite finding an enormous number of question about the same problem (1, 2, 3, 4) I have never found an answer that took performance into consideration, even here.

Although multiple working solutions has been already given I would like to do a performance consideration.

EDIT: Thanks to Manatax for pointing out that option 1 does not suffer of performance issues.

Using Option 1 and 2, aka the COLLATE cast approach, can lead to potential bottleneck, cause any index defined on the column will not be used causing a full scan.

Even though I did not try out Option 3, my hunch is that it will suffer the same consequences of option 1 and 2.

Lastly, Option 4 is the best option for very large tables when it is viable. I mean there are no other usage that rely on the original collation.

Consider this simplified query:

SELECT 
    *
FROM
    schema1.table1 AS T1
        LEFT JOIN
    schema2.table2 AS T2 ON T2.CUI = T1.CUI
WHERE
    T1.cui IN ('C0271662' , 'C2919021')
;

In my original example, I had many more joins. Of course, table1 and table2 have different collations. Using the collate operator to cast, it will lead to indexes not being used.

See sql explanation in the picture below.

Visual Query Explanation when using the COLLATE cast

On the other hand, option 4 can take advantages of possible index and led to fast queries.

In the picture below, you can see the same query being run after applied Option 4, aka altering the schema/table/column collation.

Visual Query Explanation after the collation has been changed, and therefore without the collate cast

In conclusion, if performance are important and you can alter the collation of the table, go for Option 4. If you have to act on a single column, you can use something like this:

ALTER TABLE schema1.table1 MODIFY `field` VARCHAR(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;