MYSQL错误：排序规则的非法混合

Question

i am receiving the following error message

[Err] 1267 - Illegal mix of collations (latin1_swedish_ci,IMPLICIT) and (utf8_general_ci,COERCIBLE) for operation '='

Subquery contains Union of two tables from two different databases. The query i am trying to execute is given below

 SELECT c.CORRECTION_NO FROM ( SELECT "regm2017" as `SESSION`,SERIALNO,NAME,FATHER FROM regm2017.master r17 WHERE r17.IS_DELETED=0 UNION SELECT "regm2016" as `SESSION`,SERIALNO,NAME,FATHER FROM regm2016.master r16 WHERE r16.IS_DELETED=0 ) as r JOIN corrections_registration as c ON c.SERIALNO = r.SERIALNO AND c.`SESSION`= r.`SESSION`; 

Answer 1

It happened due to variation in collation.If you give any values explicitly in Query,collation be will taken from Connection.

You can use something like this.

  SELECT c.CORRECTION_NO FROM ( SELECT "regm2017" COLLATE utf8_general_ci as > `SESSION`,SERIALNO,NAME,FATHER FROM regm2017.master r17 WHERE r17.IS_DELETED=0 UNION SELECT "regm2016" COLLATE utf8_general_ci as `SESSION`,SERIALNO,NAME,FATHER FROM regm2016.master r16 WHERE r16.IS_DELETED=0 ) as r JOIN corrections_registration as c ON c.SERIALNO = r.SERIALNO AND c.`SESSION`= r.`SESSION`;` 

OR

  SELECT c.CORRECTION_NO FROM ( SELECT "regm2017" COLLATE latin1_swedish_ci as `SESSION`,SERIALNO,NAME,FATHER FROM regm2017.master r17 WHERE r17.IS_DELETED=0 UNION SELECT "regm2016" COLLATE latin1_swedish_ci as `SESSION`,SERIALNO,NAME,FATHER FROM regm2016.master r16 WHERE r16.IS_DELETED=0 ) as r JOIN corrections_registration as c ON c.SERIALNO = r.SERIALNO AND c.`SESSION`= r.`SESSION`;