Bugs#9129: CHARSET(), COLLATION(), COERCIBILITY()

not always correct for NULL values.
Now they always result a non NULL value even
the argument is NULL. It is more usefull for 
debugging purposes.

mysql-test/r/func_str.result

@@ -512,7 +512,7 @@ collation(make_set(255,_latin2'a',_latin2'b',_latin2'c'))	coercibility(make_set(
 latin2_general_ci	4
 select collation(export_set(255,_latin2'y',_latin2'n',_latin2' ')), coercibility(export_set(255,_latin2'y',_latin2'n',_latin2' '));
 collation(export_set(255,_latin2'y',_latin2'n',_latin2' '))	coercibility(export_set(255,_latin2'y',_latin2'n',_latin2' '))
-binary	4
+latin2_general_ci	4
 select collation(trim(_latin2' a ')), coercibility(trim(_latin2' a '));
 collation(trim(_latin2' a '))	coercibility(trim(_latin2' a '))
 latin2_general_ci	4
@@ -627,6 +627,15 @@ t1	CREATE TABLE `t1` (
   `encode('abcd','ab')` binary(4) NOT NULL default ''
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 drop table t1;
+create table t1 (a char character set latin2);
+insert into t1 values (null);
+select charset(a), collation(a), coercibility(a) from t1;
+charset(a)	collation(a)	coercibility(a)
+latin2	latin2_general_ci	2
+drop table t1;
+select charset(null), collation(null), coercibility(null);
+charset(null)	collation(null)	coercibility(null)
+binary	binary	5
 select SUBSTR('abcdefg',3,2);
 SUBSTR('abcdefg',3,2)
 cd

mysql-test/t/func_str.test

@@ -368,6 +368,15 @@ select
 show create table t1;
 drop table t1;
 
+#
+# Bug#9129
+#
+create table t1 (a char character set latin2);
+insert into t1 values (null);
+select charset(a), collation(a), coercibility(a) from t1;
+drop table t1;
+select charset(null), collation(null), coercibility(null);
+
 #
 # test for SUBSTR
 #

sql/item_func.cc

@@ -1346,11 +1346,6 @@ longlong Item_func_char_length::val_int()
 longlong Item_func_coercibility::val_int()
 {
   DBUG_ASSERT(fixed == 1);
-  if (args[0]->null_value)
-  {
-    null_value= 1;
-    return 0;
-  }
   null_value= 0;
   return (longlong) args[0]->collation.derivation;
 }

sql/item_strfunc.cc

@@ -2290,12 +2290,11 @@ bool Item_func_set_collation::eq(const Item *item, bool binary_cmp) const
 String *Item_func_charset::val_str(String *str)
 {
   DBUG_ASSERT(fixed == 1);
-  String *res = args[0]->val_str(str);
   uint dummy_errors;
 
-  if ((null_value=(args[0]->null_value || !res->charset())))
-    return 0;
-  str->copy(res->charset()->csname,strlen(res->charset()->csname),
+  CHARSET_INFO *cs= args[0]->collation.collation; 
+  null_value= 0;
+  str->copy(cs->csname, strlen(cs->csname),
 	    &my_charset_latin1, collation.collation, &dummy_errors);
   return str;
 }
@@ -2303,12 +2302,11 @@ String *Item_func_charset::val_str(String *str)
 String *Item_func_collation::val_str(String *str)
 {
   DBUG_ASSERT(fixed == 1);
-  String *res = args[0]->val_str(str);
   uint dummy_errors;
+  CHARSET_INFO *cs= args[0]->collation.collation; 
 
-  if ((null_value=(args[0]->null_value || !res->charset())))
-    return 0;
-  str->copy(res->charset()->name,strlen(res->charset()->name),
+  null_value= 0;
+  str->copy(cs->name, strlen(cs->name),
 	    &my_charset_latin1, collation.collation, &dummy_errors);
   return str;
 }
@@ -2472,6 +2470,7 @@ String* Item_func_export_set::val_str(String* str)
   uint num_set_values = 64;
   ulonglong mask = 0x1;
   str->length(0);
+  str->set_charset(collation.collation);
 
   /* Check if some argument is a NULL value */
   if (args[0]->null_value || args[1]->null_value || args[2]->null_value)