Bug#9425 A user variable doesn't always have implicit coercibility

Coercibility fixes for numeric types and not defined values were done.

mysql-test/r/user_var.result

@@ -193,3 +193,10 @@ set @var= NULL ;
 select FIELD( @var,'1it','Hit') as my_column;
 my_column
 0
+select @v, coercibility(@v);
+@v	coercibility(@v)
+NULL	2
+set @v1=null, @v2=1, @v3=1.1, @v4=now();
+select coercibility(@v1),coercibility(@v2),coercibility(@v3),coercibility(@v4);
+coercibility(@v1)	coercibility(@v2)	coercibility(@v3)	coercibility(@v4)
+2	2	2	2

mysql-test/t/user_var.test

@@ -122,3 +122,10 @@ drop table t1;
 #
 set @var= NULL ;
 select FIELD( @var,'1it','Hit') as my_column;
+
+#
+# Bug#9425 A user variable doesn't always have implicit coercibility
+#
+select @v, coercibility(@v);
+set @v1=null, @v2=1, @v3=1.1, @v4=now();
+select coercibility(@v1),coercibility(@v2),coercibility(@v3),coercibility(@v4);

sql/item_func.cc

@@ -2634,20 +2634,20 @@ Item_func_set_user_var::update()
   case REAL_RESULT:
   {
     res= update_hash((void*) &save_result.vreal,sizeof(save_result.vreal),
-		     REAL_RESULT, &my_charset_bin, DERIVATION_NONE);
+		     REAL_RESULT, &my_charset_bin, DERIVATION_IMPLICIT);
     break;
   }
   case INT_RESULT:
   {
     res= update_hash((void*) &save_result.vint, sizeof(save_result.vint),
-		     INT_RESULT, &my_charset_bin, DERIVATION_NONE);
+		     INT_RESULT, &my_charset_bin, DERIVATION_IMPLICIT);
     break;
   }
   case STRING_RESULT:
   {
     if (!save_result.vstr)					// Null value
       res= update_hash((void*) 0, 0, STRING_RESULT, &my_charset_bin,
-		       DERIVATION_NONE);
+		       DERIVATION_IMPLICIT);
     else
       res= update_hash((void*) save_result.vstr->ptr(),
 		       save_result.vstr->length(), STRING_RESULT,
@@ -2870,7 +2870,10 @@ void Item_func_get_user_var::fix_length_and_dec()
     }
   }
   else
+  {
+    collation.set(&my_charset_bin, DERIVATION_IMPLICIT);
     null_value= 1;
+  }
 
   if (error)
     thd->fatal_error();