func_system.test, ctype_utf8.test, func_system.result, ctype_utf8.result:

  Prove that the queries mentioned in
  Bugs#5980: NULL requires a characterset in a union
  works fine after recent changes related to itroducing
  more coercibility level: IRNORABLE and SYSCONST.

mysql-test/r/ctype_utf8.result

@@ -871,3 +871,17 @@ drop table t1;
 select convert(_koi8r'' using utf8) < convert(_koi8r'' using utf8);
 convert(_koi8r'' using utf8) < convert(_koi8r'' using utf8)
 1
+set names latin1;
+create table t1 (a varchar(10)) character set utf8;
+insert into t1 values ('test');
+select ifnull(a,'') from t1;
+ifnull(a,'')
+test
+drop table t1;
+select repeat(_utf8'+',3) as h union select NULL;
+h
++++
+NULL
+select ifnull(NULL, _utf8'string');
+ifnull(NULL, _utf8'string')
+string

mysql-test/r/func_system.result

@@ -75,4 +75,8 @@ select * from t1 where a=database();
 a
 select * from t1 where a=user();
 a
+insert into t1 values ('a');
+select left(concat(a,version()),1) from t1;
+left(concat(a,version()),1)
+a
 drop table t1;

mysql-test/t/ctype_utf8.test

@@ -707,3 +707,14 @@ drop table t1;
 # Bug#8385: utf8_general_ci treats Cyrillic letters I and SHORT I as the same
 #
 select convert(_koi8r'' using utf8) < convert(_koi8r'' using utf8);
+
+#
+# Bugs#5980: NULL requires a characterset in a union
+#
+set names latin1;
+create table t1 (a varchar(10)) character set utf8;
+insert into t1 values ('test');
+select ifnull(a,'') from t1;
+drop table t1;
+select repeat(_utf8'+',3) as h union select NULL;
+select ifnull(NULL, _utf8'string');

mysql-test/t/func_system.test

@@ -38,4 +38,6 @@ create table t1 (a char(10)) character set latin1;
 select * from t1 where a=version();
 select * from t1 where a=database();
 select * from t1 where a=user();
+insert into t1 values ('a');
+select left(concat(a,version()),1) from t1;
 drop table t1;