MySQL – Illegal mix of collations (utf8_general_ci,COERCIBLE) and (latin1_swedish_ci,IMPLICIT) for operation ‘UNION’

If you are using mysqli, issue this command right after connecting:

$mysqli->set_charset("utf8");

This will set your connection encoding to UTF8 (same as your table uses).

With plain mysql, use this:

mysql_query("SET NAMES utf8", $conn);
mysql_query("SET CHARACTER SET utf8", $conn);

This is generally caused by comparing two strings of incompatible collation or by attempting to select data of different collation into a combined column.

The clause COLLATE allows you to specify the collation used in the query.

For example, the following WHERE clause will always give the error you posted:

WHERE 'A' COLLATE latin1_general_ci = 'A' COLLATE latin1_general_cs

Your solution is to specify a shared collation for the two columns within the query. Here is an example that uses the COLLATE clause:

SELECT * FROM table ORDER BY key COLLATE latin1_general_ci;

Another option is to use the BINARY operator:

BINARY str is the shorthand for CAST(str AS BINARY).

Your solution might look something like this:

SELECT * FROM table WHERE BINARY a = BINARY b;

or,

SELECT * FROM table ORDER BY BINARY a;