item_func.cc:

set_var.cc:
variables.result
variables.test

  Bug #10904 Illegal mix of collations between a system variable and a constant
  Changing coercibility of system variables to SYSCONST,
  to be the same with USER(), DATABASE(), etc.

mysql-test/r/variables.result

@@ -210,6 +210,12 @@ query_prealloc_size	8192
 range_alloc_block_size	2048
 transaction_alloc_block_size	8192
 transaction_prealloc_size	4096
+SELECT @@version LIKE 'non-existent';
+@@version LIKE 'non-existent'
+0
+SELECT @@version_compile_os LIKE 'non-existent';
+@@version_compile_os LIKE 'non-existent'
+0
 set big_tables=OFFF;
 ERROR 42000: Variable 'big_tables' can't be set to the value of 'OFFF'
 set big_tables="OFFF";

mysql-test/t/variables.test

@@ -115,6 +115,13 @@ set @@query_alloc_block_size=default, @@query_prealloc_size=default;
 set transaction_alloc_block_size=default, @@transaction_prealloc_size=default;
 show variables like '%alloc%';
 
+#
+# Bug #10904 Illegal mix of collations between
+# a system variable and a constant
+#
+SELECT @@version LIKE 'non-existent';
+SELECT @@version_compile_os LIKE 'non-existent';
+
 # The following should give errors
 
 --error 1231

sql/item_func.cc

@@ -3369,7 +3369,7 @@ Item *get_system_var(THD *thd, enum_var_type var_type, LEX_STRING name,
       !my_strcasecmp(system_charset_info, name.str, "VERSION"))
     return new Item_string("@@VERSION", server_version,
 			   (uint) strlen(server_version),
-			   system_charset_info);
+			   system_charset_info, DERIVATION_SYSCONST);
 
   Item *item;
   sys_var *var;

sql/set_var.cc

@@ -1606,7 +1606,8 @@ Item *sys_var::item(THD *thd, enum_var_type var_type, LEX_STRING *base)
     Item_string *tmp;
     pthread_mutex_lock(&LOCK_global_system_variables);
     char *str= (char*) value_ptr(thd, var_type, base);
-    tmp= new Item_string(str, strlen(str), system_charset_info);
+    tmp= new Item_string(str, strlen(str),
+                         system_charset_info, DERIVATION_SYSCONST);
     pthread_mutex_unlock(&LOCK_global_system_variables);
     return tmp;
   }