type_blob.result, func_system.result, func_str.result, ctype_collate.result:

  fixing test results accordingly.
func_system.test:
  New test that illegal mix of collations does not happen anymore.
item_strfunc.h:
    safe_charset_converter() was added for system constants.
item_strfunc.cc:
  safe_charset_converter() was added for system constants.
item_func.cc, item.h, item.cc:
  Bug#8291: Illegal collation mix with USER() function.
  After discussion with PeterG and Serge, a new coercibility
  level for "system constants" was introduced, between
  COERRIBLE and IMPLICIT. Thus:
  SELECT col1 = USER() FROM t1; - is done according to col1 collation.
  SELECT 'string' = USER(); - is done according to USER() collation.
  At the same time, "nagg" and "strong" members were removed as unused.
item_create.cc:
  Version is a system constant too.

mysql-test/r/ctype_collate.result

@@ -514,7 +514,7 @@ Variable_name	Value
 character_set_client	latin1
 SELECT charset('a'),collation('a'),coercibility('a'),'a'='A';
 charset('a')	collation('a')	coercibility('a')	'a'='A'
-latin1	latin1_swedish_ci	3	1
+latin1	latin1_swedish_ci	4	1
 explain extended SELECT charset('a'),collation('a'),coercibility('a'),'a'='A';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
@@ -525,7 +525,7 @@ SHOW VARIABLES LIKE 'collation_client';
 Variable_name	Value
 SELECT charset('a'),collation('a'),coercibility('a'),'a'='A';
 charset('a')	collation('a')	coercibility('a')	'a'='A'
-latin1	latin1_swedish_ci	3	1
+latin1	latin1_swedish_ci	4	1
 SET CHARACTER SET 'DEFAULT';
 ERROR 42000: Unknown character set: 'DEFAULT'
 DROP TABLE t1;

mysql-test/r/func_str.result

@@ -464,97 +464,97 @@ select _latin1'B' COLLATE latin1_general_ci in (_latin1'a',_latin1'b' COLLATE la
 ERROR HY000: Illegal mix of collations (latin1_general_ci,EXPLICIT), (latin1_swedish_ci,COERCIBLE), (latin1_bin,EXPLICIT) for operation ' IN '
 select collation(bin(130)), coercibility(bin(130));
 collation(bin(130))	coercibility(bin(130))
-latin1_swedish_ci	3
+latin1_swedish_ci	4
 select collation(oct(130)), coercibility(oct(130));
 collation(oct(130))	coercibility(oct(130))
-latin1_swedish_ci	3
+latin1_swedish_ci	4
 select collation(conv(130,16,10)), coercibility(conv(130,16,10));
 collation(conv(130,16,10))	coercibility(conv(130,16,10))
-latin1_swedish_ci	3
+latin1_swedish_ci	4
 select collation(hex(130)), coercibility(hex(130));
 collation(hex(130))	coercibility(hex(130))
-latin1_swedish_ci	3
+latin1_swedish_ci	4
 select collation(char(130)), coercibility(hex(130));
 collation(char(130))	coercibility(hex(130))
-latin1_swedish_ci	3
+latin1_swedish_ci	4
 select collation(format(130,10)), coercibility(format(130,10));
 collation(format(130,10))	coercibility(format(130,10))
-latin1_swedish_ci	3
+latin1_swedish_ci	4
 select collation(lcase(_latin2'a')), coercibility(lcase(_latin2'a'));
 collation(lcase(_latin2'a'))	coercibility(lcase(_latin2'a'))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(ucase(_latin2'a')), coercibility(ucase(_latin2'a'));
 collation(ucase(_latin2'a'))	coercibility(ucase(_latin2'a'))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(left(_latin2'a',1)), coercibility(left(_latin2'a',1));
 collation(left(_latin2'a',1))	coercibility(left(_latin2'a',1))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(right(_latin2'a',1)), coercibility(right(_latin2'a',1));
 collation(right(_latin2'a',1))	coercibility(right(_latin2'a',1))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(substring(_latin2'a',1,1)), coercibility(substring(_latin2'a',1,1));
 collation(substring(_latin2'a',1,1))	coercibility(substring(_latin2'a',1,1))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(concat(_latin2'a',_latin2'b')), coercibility(concat(_latin2'a',_latin2'b'));
 collation(concat(_latin2'a',_latin2'b'))	coercibility(concat(_latin2'a',_latin2'b'))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(lpad(_latin2'a',4,_latin2'b')), coercibility(lpad(_latin2'a',4,_latin2'b'));
 collation(lpad(_latin2'a',4,_latin2'b'))	coercibility(lpad(_latin2'a',4,_latin2'b'))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(rpad(_latin2'a',4,_latin2'b')), coercibility(rpad(_latin2'a',4,_latin2'b'));
 collation(rpad(_latin2'a',4,_latin2'b'))	coercibility(rpad(_latin2'a',4,_latin2'b'))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(concat_ws(_latin2'a',_latin2'b')), coercibility(concat_ws(_latin2'a',_latin2'b'));
 collation(concat_ws(_latin2'a',_latin2'b'))	coercibility(concat_ws(_latin2'a',_latin2'b'))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(make_set(255,_latin2'a',_latin2'b',_latin2'c')), coercibility(make_set(255,_latin2'a',_latin2'b',_latin2'c'));
 collation(make_set(255,_latin2'a',_latin2'b',_latin2'c'))	coercibility(make_set(255,_latin2'a',_latin2'b',_latin2'c'))
-latin2_general_ci	3
+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	3
+binary	4
 select collation(trim(_latin2' a ')), coercibility(trim(_latin2' a '));
 collation(trim(_latin2' a '))	coercibility(trim(_latin2' a '))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(ltrim(_latin2' a ')), coercibility(ltrim(_latin2' a '));
 collation(ltrim(_latin2' a '))	coercibility(ltrim(_latin2' a '))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(rtrim(_latin2' a ')), coercibility(rtrim(_latin2' a '));
 collation(rtrim(_latin2' a '))	coercibility(rtrim(_latin2' a '))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(trim(LEADING _latin2' ' FROM _latin2'a')), coercibility(trim(LEADING _latin2'a' FROM _latin2'a'));
 collation(trim(LEADING _latin2' ' FROM _latin2'a'))	coercibility(trim(LEADING _latin2'a' FROM _latin2'a'))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(trim(TRAILING _latin2' ' FROM _latin2'a')), coercibility(trim(TRAILING _latin2'a' FROM _latin2'a'));
 collation(trim(TRAILING _latin2' ' FROM _latin2'a'))	coercibility(trim(TRAILING _latin2'a' FROM _latin2'a'))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(trim(BOTH _latin2' ' FROM _latin2'a')), coercibility(trim(BOTH _latin2'a' FROM _latin2'a'));
 collation(trim(BOTH _latin2' ' FROM _latin2'a'))	coercibility(trim(BOTH _latin2'a' FROM _latin2'a'))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(repeat(_latin2'a',10)), coercibility(repeat(_latin2'a',10));
 collation(repeat(_latin2'a',10))	coercibility(repeat(_latin2'a',10))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(reverse(_latin2'ab')), coercibility(reverse(_latin2'ab'));
 collation(reverse(_latin2'ab'))	coercibility(reverse(_latin2'ab'))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(quote(_latin2'ab')), coercibility(quote(_latin2'ab'));
 collation(quote(_latin2'ab'))	coercibility(quote(_latin2'ab'))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(soundex(_latin2'ab')), coercibility(soundex(_latin2'ab'));
 collation(soundex(_latin2'ab'))	coercibility(soundex(_latin2'ab'))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(substring(_latin2'ab',1)), coercibility(substring(_latin2'ab',1));
 collation(substring(_latin2'ab',1))	coercibility(substring(_latin2'ab',1))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(insert(_latin2'abcd',2,3,_latin2'ef')), coercibility(insert(_latin2'abcd',2,3,_latin2'ef'));
 collation(insert(_latin2'abcd',2,3,_latin2'ef'))	coercibility(insert(_latin2'abcd',2,3,_latin2'ef'))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(replace(_latin2'abcd',_latin2'b',_latin2'B')), coercibility(replace(_latin2'abcd',_latin2'b',_latin2'B'));
 collation(replace(_latin2'abcd',_latin2'b',_latin2'B'))	coercibility(replace(_latin2'abcd',_latin2'b',_latin2'B'))
-latin2_general_ci	3
+latin2_general_ci	4
 select collation(encode('abcd','ab')), coercibility(encode('abcd','ab'));
 collation(encode('abcd','ab'))	coercibility(encode('abcd','ab'))
-binary	3
+binary	4
 create table t1 
 select
 bin(130),

mysql-test/r/func_system.result

@@ -68,3 +68,11 @@ drop table t1;
 select TRUE,FALSE,NULL;
 TRUE	FALSE	NULL
 1	0	NULL
+create table t1 (a char(10)) character set latin1;
+select * from t1 where a=version();
+a
+select * from t1 where a=database();
+a
+select * from t1 where a=user();
+a
+drop table t1;

mysql-test/r/type_blob.result

@@ -499,7 +499,7 @@ charset(load_file('../../std_data/words.dat')),
 collation(load_file('../../std_data/words.dat')),
 coercibility(load_file('../../std_data/words.dat'));
 charset(load_file('../../std_data/words.dat'))	collation(load_file('../../std_data/words.dat'))	coercibility(load_file('../../std_data/words.dat'))
-binary	binary	3
+binary	binary	4
 explain extended select 
 charset(load_file('../../std_data/words.dat')),
 collation(load_file('../../std_data/words.dat')),

mysql-test/t/func_system.test

@@ -30,3 +30,12 @@ show create table t1;
 drop table t1;
 
 select TRUE,FALSE,NULL;
+
+#
+# Bug#8291 Illegal collation mix with USER() function
+#
+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();
+drop table t1;

sql/item.cc

@@ -384,7 +384,6 @@ void Item::split_sum_func2(THD *thd, Item **ref_pointer_array,
 */
 bool DTCollation::aggregate(DTCollation &dt, uint flags)
 {
-  nagg++;
   if (!my_charset_same(collation, dt.collation))
   {
     /* 
@@ -400,7 +399,6 @@ bool DTCollation::aggregate(DTCollation &dt, uint flags)
       else
       {
 	set(dt); 
-        strong= nagg;
       }
     }
     else if (dt.collation == &my_charset_bin)
@@ -408,7 +406,6 @@ bool DTCollation::aggregate(DTCollation &dt, uint flags)
       if (dt.derivation <= derivation)
       {
         set(dt);
-        strong= nagg;
       }
       else
        ; // Do nothing
@@ -424,20 +421,18 @@ bool DTCollation::aggregate(DTCollation &dt, uint flags)
              dt.collation->state & MY_CS_UNICODE)
     {
       set(dt);
-      strong= nagg;
     }
     else if ((flags & MY_COLL_ALLOW_COERCIBLE_CONV) &&
              derivation < dt.derivation &&
-             dt.derivation >= DERIVATION_COERCIBLE)
+             dt.derivation >= DERIVATION_SYSCONST)
     {
       // Do nothing;
     }
     else if ((flags & MY_COLL_ALLOW_COERCIBLE_CONV) &&
              dt.derivation < derivation &&
-             derivation >= DERIVATION_COERCIBLE)
+             derivation >= DERIVATION_SYSCONST)
     {
       set(dt);
-      strong= nagg;
     }
     else
     {
@@ -453,7 +448,6 @@ bool DTCollation::aggregate(DTCollation &dt, uint flags)
   else if (dt.derivation < derivation)
   {
     set(dt);
-    strong= nagg;
   }
   else
   { 

sql/item.h

@@ -31,8 +31,9 @@ void item_init(void);			/* Init item functions */
 
 enum Derivation
 {
-  DERIVATION_IGNORABLE= 4,
-  DERIVATION_COERCIBLE= 3,
+  DERIVATION_IGNORABLE= 5,
+  DERIVATION_COERCIBLE= 4,
+  DERIVATION_SYSCONST= 3,
   DERIVATION_IMPLICIT= 2,
   DERIVATION_NONE= 1,
   DERIVATION_EXPLICIT= 0
@@ -61,22 +62,16 @@ class DTCollation {
 public:
   CHARSET_INFO     *collation;
   enum Derivation derivation;
-  uint nagg;    // Total number of aggregated collations.
-  uint strong;  // Number of the strongest collation.
   
   DTCollation()
   {
     collation= &my_charset_bin;
     derivation= DERIVATION_NONE;
-    nagg= 0;
-    strong= 0;
   }
   DTCollation(CHARSET_INFO *collation_arg, Derivation derivation_arg)
   {
     collation= collation_arg;
     derivation= derivation_arg;
-    nagg= 0;
-    strong= 0;
   }
   void set(DTCollation &dt)
   { 
@@ -102,6 +97,7 @@ class DTCollation {
       case DERIVATION_IGNORABLE: return "IGNORABLE";
       case DERIVATION_COERCIBLE: return "COERCIBLE";
       case DERIVATION_IMPLICIT:  return "IMPLICIT";
+      case DERIVATION_SYSCONST:  return "SYSCONST";
       case DERIVATION_EXPLICIT:  return "EXPLICIT";
       case DERIVATION_NONE:      return "NONE";
       default: return "UNKNOWN";

sql/item_create.cc

@@ -441,7 +441,7 @@ Item *create_func_version(void)
 {
   return new Item_string(NullS,server_version, 
 			 (uint) strlen(server_version),
-			 system_charset_info, DERIVATION_IMPLICIT);
+			 system_charset_info, DERIVATION_SYSCONST);
 }
 
 Item *create_func_weekday(Item* a)

sql/item_func.cc

@@ -79,8 +79,6 @@ bool Item_func::agg_arg_collations(DTCollation &c, Item **av, uint count,
                                    uint flags)
 {
   uint i;
-  c.nagg= 0;
-  c.strong= 0;
   c.set(av[0]->collation);
   for (i= 1; i < count; i++)
   {

sql/item_strfunc.cc

@@ -1509,6 +1509,23 @@ String *Item_func_decode::val_str(String *str)
 }
 
 
+Item *Item_func_sysconst::safe_charset_converter(CHARSET_INFO *tocs)
+{
+  Item_string *conv;
+  uint conv_errors;
+  String tmp, cstr, *ostr= val_str(&tmp);
+  cstr.copy(ostr->ptr(), ostr->length(), ostr->charset(), tocs, &conv_errors);
+  if (conv_errors || !(conv= new Item_string(cstr.ptr(), cstr.length(),
+                                             cstr.charset(),
+                                             collation.derivation)))
+  {
+    return NULL;
+  }
+  conv->str_value.copy();
+  return conv;
+}
+
+
 String *Item_func_database::val_str(String *str)
 {
   DBUG_ASSERT(fixed == 1);

sql/item_strfunc.h

@@ -337,10 +337,18 @@ class Item_func_decode :public Item_func_encode
 };
 
 
-class Item_func_database :public Item_str_func
+class Item_func_sysconst :public Item_str_func
 {
 public:
-  Item_func_database() { collation.set(system_charset_info,DERIVATION_IMPLICIT); }
+  Item_func_sysconst()
+  { collation.set(system_charset_info,DERIVATION_SYSCONST); }
+  Item *safe_charset_converter(CHARSET_INFO *tocs);
+};
+
+class Item_func_database :public Item_func_sysconst
+{
+public:
+  Item_func_database() :Item_func_sysconst() {}
   String *val_str(String *);
   void fix_length_and_dec()
   {
@@ -350,10 +358,10 @@ class Item_func_database :public Item_str_func
   const char *func_name() const { return "database"; }
 };
 
-class Item_func_user :public Item_str_func
+class Item_func_user :public Item_func_sysconst
 {
 public:
-  Item_func_user() { collation.set(system_charset_info, DERIVATION_IMPLICIT); }
+  Item_func_user() :Item_func_sysconst() {}
   String *val_str(String *);
   void fix_length_and_dec() 
   {